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![Johannes Weiner](/assets/img/avatar_default.png)
The page cache and most shrinkable slab caches hold data that has been read from disk, but there are some caches that only cache CPU work, such as the dentry and inode caches of procfs and sysfs, as well as the subset of radix tree nodes that track non-resident page cache. Currently, all these are shrunk at the same rate: using DEFAULT_SEEKS for the shrinker's seeks setting tells the reclaim algorithm that for every two page cache pages scanned it should scan one slab object. This is a bogus setting. A virtual inode that required no IO to create is not twice as valuable as a page cache page; shadow cache entries with eviction distances beyond the size of memory aren't either. In most cases, the behavior in practice is still fine. Such virtual caches don't tend to grow and assert themselves aggressively, and usually get picked up before they cause problems. But there are scenarios where that's not true. Our database workloads suffer from two of those. For one, their file workingset is several times bigger than available memory, which has the kernel aggressively create shadow page cache entries for the non-resident parts of it. The workingset code does tell the VM that most of these are expendable, but the VM ends up balancing them 2:1 to cache pages as per the seeks setting. This is a huge waste of memory. These workloads also deal with tens of thousands of open files and use /proc for introspection, which ends up growing the proc_inode_cache to absurdly large sizes - again at the cost of valuable cache space, which isn't a reasonable trade-off, given that proc inodes can be re-created without involving the disk. This patch implements a "zero-seek" setting for shrinkers that results in a target ratio of 0:1 between their objects and IO-backed caches. This allows such virtual caches to grow when memory is available (they do cache/avoid CPU work after all), but effectively disables them as soon as IO-backed objects are under pressure. It then switches the shrinkers for procfs and sysfs metadata, as well as excess page cache shadow nodes, to the new zero-seek setting. Link: http://lkml.kernel.org/r/20181009184732.762-5-hannes@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reported-by: Domas Mituzas <dmituzas@fb.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Rik van Riel <riel@surriel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
420 lines
11 KiB
C
420 lines
11 KiB
C
/*
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* fs/kernfs/mount.c - kernfs mount implementation
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*
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* Copyright (c) 2001-3 Patrick Mochel
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* Copyright (c) 2007 SUSE Linux Products GmbH
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* Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
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*
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* This file is released under the GPLv2.
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*/
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/init.h>
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#include <linux/magic.h>
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#include <linux/slab.h>
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#include <linux/pagemap.h>
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#include <linux/namei.h>
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#include <linux/seq_file.h>
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#include <linux/exportfs.h>
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#include "kernfs-internal.h"
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struct kmem_cache *kernfs_node_cache;
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static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
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{
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struct kernfs_root *root = kernfs_info(sb)->root;
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->remount_fs)
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return scops->remount_fs(root, flags, data);
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return 0;
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}
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static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
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{
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struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->show_options)
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return scops->show_options(sf, root);
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return 0;
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}
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static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
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{
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struct kernfs_node *node = kernfs_dentry_node(dentry);
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struct kernfs_root *root = kernfs_root(node);
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->show_path)
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return scops->show_path(sf, node, root);
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seq_dentry(sf, dentry, " \t\n\\");
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return 0;
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}
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const struct super_operations kernfs_sops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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.evict_inode = kernfs_evict_inode,
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.remount_fs = kernfs_sop_remount_fs,
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.show_options = kernfs_sop_show_options,
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.show_path = kernfs_sop_show_path,
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};
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/*
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* Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
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* number and generation
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*/
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struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
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const union kernfs_node_id *id)
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{
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struct kernfs_node *kn;
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kn = kernfs_find_and_get_node_by_ino(root, id->ino);
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if (!kn)
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return NULL;
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if (kn->id.generation != id->generation) {
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kernfs_put(kn);
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return NULL;
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}
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return kn;
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}
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static struct inode *kernfs_fh_get_inode(struct super_block *sb,
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u64 ino, u32 generation)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct inode *inode;
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struct kernfs_node *kn;
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if (ino == 0)
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return ERR_PTR(-ESTALE);
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kn = kernfs_find_and_get_node_by_ino(info->root, ino);
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if (!kn)
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return ERR_PTR(-ESTALE);
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inode = kernfs_get_inode(sb, kn);
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kernfs_put(kn);
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if (!inode)
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return ERR_PTR(-ESTALE);
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if (generation && inode->i_generation != generation) {
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/* we didn't find the right inode.. */
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iput(inode);
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return ERR_PTR(-ESTALE);
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}
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return inode;
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}
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static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
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int fh_len, int fh_type)
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{
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return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
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kernfs_fh_get_inode);
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}
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static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
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int fh_len, int fh_type)
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{
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return generic_fh_to_parent(sb, fid, fh_len, fh_type,
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kernfs_fh_get_inode);
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}
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static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
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{
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struct kernfs_node *kn = kernfs_dentry_node(child);
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return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
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}
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static const struct export_operations kernfs_export_ops = {
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.fh_to_dentry = kernfs_fh_to_dentry,
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.fh_to_parent = kernfs_fh_to_parent,
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.get_parent = kernfs_get_parent_dentry,
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};
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/**
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* kernfs_root_from_sb - determine kernfs_root associated with a super_block
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* @sb: the super_block in question
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*
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* Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
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* %NULL is returned.
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*/
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struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
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{
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if (sb->s_op == &kernfs_sops)
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return kernfs_info(sb)->root;
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return NULL;
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}
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/*
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* find the next ancestor in the path down to @child, where @parent was the
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* ancestor whose descendant we want to find.
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*
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* Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
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* node. If @parent is b, then we return the node for c.
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* Passing in d as @parent is not ok.
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*/
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static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
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struct kernfs_node *parent)
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{
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if (child == parent) {
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pr_crit_once("BUG in find_next_ancestor: called with parent == child");
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return NULL;
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}
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while (child->parent != parent) {
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if (!child->parent)
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return NULL;
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child = child->parent;
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}
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return child;
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}
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/**
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* kernfs_node_dentry - get a dentry for the given kernfs_node
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* @kn: kernfs_node for which a dentry is needed
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* @sb: the kernfs super_block
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*/
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struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
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struct super_block *sb)
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{
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struct dentry *dentry;
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struct kernfs_node *knparent = NULL;
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BUG_ON(sb->s_op != &kernfs_sops);
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dentry = dget(sb->s_root);
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/* Check if this is the root kernfs_node */
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if (!kn->parent)
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return dentry;
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knparent = find_next_ancestor(kn, NULL);
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if (WARN_ON(!knparent))
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return ERR_PTR(-EINVAL);
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do {
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struct dentry *dtmp;
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struct kernfs_node *kntmp;
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if (kn == knparent)
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return dentry;
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kntmp = find_next_ancestor(kn, knparent);
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if (WARN_ON(!kntmp))
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return ERR_PTR(-EINVAL);
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dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
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strlen(kntmp->name));
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dput(dentry);
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if (IS_ERR(dtmp))
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return dtmp;
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knparent = kntmp;
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dentry = dtmp;
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} while (true);
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}
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static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct inode *inode;
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struct dentry *root;
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info->sb = sb;
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/* Userspace would break if executables or devices appear on sysfs */
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sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
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sb->s_blocksize = PAGE_SIZE;
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sb->s_blocksize_bits = PAGE_SHIFT;
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sb->s_magic = magic;
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sb->s_op = &kernfs_sops;
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sb->s_xattr = kernfs_xattr_handlers;
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if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
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sb->s_export_op = &kernfs_export_ops;
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sb->s_time_gran = 1;
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/* sysfs dentries and inodes don't require IO to create */
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sb->s_shrink.seeks = 0;
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/* get root inode, initialize and unlock it */
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mutex_lock(&kernfs_mutex);
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inode = kernfs_get_inode(sb, info->root->kn);
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mutex_unlock(&kernfs_mutex);
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if (!inode) {
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pr_debug("kernfs: could not get root inode\n");
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return -ENOMEM;
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}
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/* instantiate and link root dentry */
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root = d_make_root(inode);
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if (!root) {
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pr_debug("%s: could not get root dentry!\n", __func__);
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return -ENOMEM;
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}
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sb->s_root = root;
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sb->s_d_op = &kernfs_dops;
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return 0;
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}
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static int kernfs_test_super(struct super_block *sb, void *data)
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{
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struct kernfs_super_info *sb_info = kernfs_info(sb);
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struct kernfs_super_info *info = data;
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return sb_info->root == info->root && sb_info->ns == info->ns;
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}
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static int kernfs_set_super(struct super_block *sb, void *data)
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{
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int error;
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error = set_anon_super(sb, data);
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if (!error)
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sb->s_fs_info = data;
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return error;
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}
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/**
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* kernfs_super_ns - determine the namespace tag of a kernfs super_block
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* @sb: super_block of interest
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*
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* Return the namespace tag associated with kernfs super_block @sb.
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*/
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const void *kernfs_super_ns(struct super_block *sb)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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return info->ns;
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}
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/**
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* kernfs_mount_ns - kernfs mount helper
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* @fs_type: file_system_type of the fs being mounted
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* @flags: mount flags specified for the mount
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* @root: kernfs_root of the hierarchy being mounted
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* @magic: file system specific magic number
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* @new_sb_created: tell the caller if we allocated a new superblock
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* @ns: optional namespace tag of the mount
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*
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* This is to be called from each kernfs user's file_system_type->mount()
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* implementation, which should pass through the specified @fs_type and
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* @flags, and specify the hierarchy and namespace tag to mount via @root
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* and @ns, respectively.
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*
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* The return value can be passed to the vfs layer verbatim.
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*/
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struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
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struct kernfs_root *root, unsigned long magic,
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bool *new_sb_created, const void *ns)
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{
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struct super_block *sb;
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struct kernfs_super_info *info;
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int error;
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info = kzalloc(sizeof(*info), GFP_KERNEL);
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if (!info)
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return ERR_PTR(-ENOMEM);
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info->root = root;
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info->ns = ns;
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INIT_LIST_HEAD(&info->node);
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sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
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&init_user_ns, info);
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if (IS_ERR(sb) || sb->s_fs_info != info)
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kfree(info);
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if (IS_ERR(sb))
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return ERR_CAST(sb);
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if (new_sb_created)
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*new_sb_created = !sb->s_root;
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if (!sb->s_root) {
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struct kernfs_super_info *info = kernfs_info(sb);
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error = kernfs_fill_super(sb, magic);
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if (error) {
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deactivate_locked_super(sb);
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return ERR_PTR(error);
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}
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sb->s_flags |= SB_ACTIVE;
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mutex_lock(&kernfs_mutex);
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list_add(&info->node, &root->supers);
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mutex_unlock(&kernfs_mutex);
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}
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return dget(sb->s_root);
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}
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/**
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* kernfs_kill_sb - kill_sb for kernfs
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* @sb: super_block being killed
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*
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* This can be used directly for file_system_type->kill_sb(). If a kernfs
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* user needs extra cleanup, it can implement its own kill_sb() and call
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* this function at the end.
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*/
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void kernfs_kill_sb(struct super_block *sb)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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mutex_lock(&kernfs_mutex);
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list_del(&info->node);
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mutex_unlock(&kernfs_mutex);
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/*
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* Remove the superblock from fs_supers/s_instances
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* so we can't find it, before freeing kernfs_super_info.
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*/
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kill_anon_super(sb);
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kfree(info);
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}
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/**
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* kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
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* @kernfs_root: the kernfs_root in question
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* @ns: the namespace tag
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*
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* Pin the superblock so the superblock won't be destroyed in subsequent
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* operations. This can be used to block ->kill_sb() which may be useful
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* for kernfs users which dynamically manage superblocks.
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*
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* Returns NULL if there's no superblock associated to this kernfs_root, or
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* -EINVAL if the superblock is being freed.
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*/
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struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
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{
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struct kernfs_super_info *info;
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struct super_block *sb = NULL;
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mutex_lock(&kernfs_mutex);
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list_for_each_entry(info, &root->supers, node) {
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if (info->ns == ns) {
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sb = info->sb;
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if (!atomic_inc_not_zero(&info->sb->s_active))
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sb = ERR_PTR(-EINVAL);
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break;
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}
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}
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mutex_unlock(&kernfs_mutex);
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return sb;
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}
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void __init kernfs_init(void)
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{
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/*
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* the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
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* can access the slab lock free. This could introduce stale nodes,
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* please see how kernfs_find_and_get_node_by_ino filters out stale
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* nodes.
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*/
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kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
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sizeof(struct kernfs_node),
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0,
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SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
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NULL);
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}
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