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![Mel Gorman](/assets/img/avatar_default.png)
Currently swapfiles are managed entirely by the core VM by using ->bmap to allocate space and write to the blocks directly. This effectively ensures that the underlying blocks are allocated and avoids the need for the swap subsystem to locate what physical blocks store offsets within a file. If the swap subsystem is to use the filesystem information to locate the blocks, it is critical that information such as block groups, block bitmaps and the block descriptor table that map the swap file were resident in memory. This patch adds address_space_operations that the VM can call when activating or deactivating swap backed by a file. int swap_activate(struct file *); int swap_deactivate(struct file *); The ->swap_activate() method is used to communicate to the file that the VM relies on it, and the address_space should take adequate measures such as reserving space in the underlying device, reserving memory for mempools and pinning information such as the block descriptor table in memory. The ->swap_deactivate() method is called on sys_swapoff() if ->swap_activate() returned success. After a successful swapfile ->swap_activate, the swapfile is marked SWP_FILE and swapper_space.a_ops will proxy to sis->swap_file->f_mappings->a_ops using ->direct_io to write swapcache pages and ->readpage to read. It is perfectly possible that direct_IO be used to read the swap pages but it is an unnecessary complication. Similarly, it is possible that ->writepage be used instead of direct_io to write the pages but filesystem developers have stated that calling writepage from the VM is undesirable for a variety of reasons and using direct_IO opens up the possibility of writing back batches of swap pages in the future. [a.p.zijlstra@chello.nl: Original patch] Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Rik van Riel <riel@redhat.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David S. Miller <davem@davemloft.net> Cc: Eric B Munson <emunson@mgebm.net> Cc: Eric Paris <eparis@redhat.com> Cc: James Morris <jmorris@namei.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Christie <michaelc@cs.wisc.edu> Cc: Neil Brown <neilb@suse.de> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc> Cc: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: Xiaotian Feng <dfeng@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
401 lines
10 KiB
C
401 lines
10 KiB
C
/*
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* linux/mm/swap_state.c
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*
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* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
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* Swap reorganised 29.12.95, Stephen Tweedie
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*
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* Rewritten to use page cache, (C) 1998 Stephen Tweedie
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*/
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#include <linux/mm.h>
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#include <linux/gfp.h>
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#include <linux/kernel_stat.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/init.h>
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#include <linux/pagemap.h>
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#include <linux/backing-dev.h>
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#include <linux/blkdev.h>
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#include <linux/pagevec.h>
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#include <linux/migrate.h>
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#include <linux/page_cgroup.h>
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#include <asm/pgtable.h>
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/*
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* swapper_space is a fiction, retained to simplify the path through
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* vmscan's shrink_page_list.
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*/
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static const struct address_space_operations swap_aops = {
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.writepage = swap_writepage,
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.set_page_dirty = swap_set_page_dirty,
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.migratepage = migrate_page,
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};
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static struct backing_dev_info swap_backing_dev_info = {
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.name = "swap",
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.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
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};
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struct address_space swapper_space = {
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.page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
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.tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
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.a_ops = &swap_aops,
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.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
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.backing_dev_info = &swap_backing_dev_info,
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};
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#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
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static struct {
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unsigned long add_total;
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unsigned long del_total;
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unsigned long find_success;
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unsigned long find_total;
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} swap_cache_info;
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void show_swap_cache_info(void)
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{
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printk("%lu pages in swap cache\n", total_swapcache_pages);
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printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
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swap_cache_info.add_total, swap_cache_info.del_total,
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swap_cache_info.find_success, swap_cache_info.find_total);
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printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
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printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
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}
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/*
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* __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
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* but sets SwapCache flag and private instead of mapping and index.
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*/
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static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
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{
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int error;
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(PageSwapCache(page));
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VM_BUG_ON(!PageSwapBacked(page));
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page_cache_get(page);
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SetPageSwapCache(page);
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set_page_private(page, entry.val);
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spin_lock_irq(&swapper_space.tree_lock);
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error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
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if (likely(!error)) {
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total_swapcache_pages++;
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__inc_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(add_total);
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}
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spin_unlock_irq(&swapper_space.tree_lock);
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if (unlikely(error)) {
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/*
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* Only the context which have set SWAP_HAS_CACHE flag
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* would call add_to_swap_cache().
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* So add_to_swap_cache() doesn't returns -EEXIST.
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*/
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VM_BUG_ON(error == -EEXIST);
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set_page_private(page, 0UL);
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ClearPageSwapCache(page);
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page_cache_release(page);
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}
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return error;
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}
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int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
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{
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int error;
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error = radix_tree_preload(gfp_mask);
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if (!error) {
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error = __add_to_swap_cache(page, entry);
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radix_tree_preload_end();
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}
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return error;
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}
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/*
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* This must be called only on pages that have
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* been verified to be in the swap cache.
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*/
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void __delete_from_swap_cache(struct page *page)
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{
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(!PageSwapCache(page));
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VM_BUG_ON(PageWriteback(page));
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radix_tree_delete(&swapper_space.page_tree, page_private(page));
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set_page_private(page, 0);
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ClearPageSwapCache(page);
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total_swapcache_pages--;
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__dec_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(del_total);
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}
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/**
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* add_to_swap - allocate swap space for a page
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* @page: page we want to move to swap
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*
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* Allocate swap space for the page and add the page to the
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* swap cache. Caller needs to hold the page lock.
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*/
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int add_to_swap(struct page *page)
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{
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swp_entry_t entry;
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int err;
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(!PageUptodate(page));
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entry = get_swap_page();
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if (!entry.val)
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return 0;
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if (unlikely(PageTransHuge(page)))
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if (unlikely(split_huge_page(page))) {
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swapcache_free(entry, NULL);
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return 0;
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}
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/*
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* Radix-tree node allocations from PF_MEMALLOC contexts could
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* completely exhaust the page allocator. __GFP_NOMEMALLOC
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* stops emergency reserves from being allocated.
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*
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* TODO: this could cause a theoretical memory reclaim
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* deadlock in the swap out path.
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*/
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/*
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* Add it to the swap cache and mark it dirty
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*/
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err = add_to_swap_cache(page, entry,
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__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
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if (!err) { /* Success */
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SetPageDirty(page);
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return 1;
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} else { /* -ENOMEM radix-tree allocation failure */
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/*
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* add_to_swap_cache() doesn't return -EEXIST, so we can safely
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* clear SWAP_HAS_CACHE flag.
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*/
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swapcache_free(entry, NULL);
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return 0;
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}
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}
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/*
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* This must be called only on pages that have
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* been verified to be in the swap cache and locked.
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* It will never put the page into the free list,
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* the caller has a reference on the page.
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*/
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void delete_from_swap_cache(struct page *page)
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{
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swp_entry_t entry;
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entry.val = page_private(page);
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spin_lock_irq(&swapper_space.tree_lock);
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__delete_from_swap_cache(page);
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spin_unlock_irq(&swapper_space.tree_lock);
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swapcache_free(entry, page);
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page_cache_release(page);
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}
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/*
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* If we are the only user, then try to free up the swap cache.
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*
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* Its ok to check for PageSwapCache without the page lock
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* here because we are going to recheck again inside
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* try_to_free_swap() _with_ the lock.
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* - Marcelo
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*/
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static inline void free_swap_cache(struct page *page)
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{
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if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
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try_to_free_swap(page);
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unlock_page(page);
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}
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}
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/*
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* Perform a free_page(), also freeing any swap cache associated with
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* this page if it is the last user of the page.
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*/
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void free_page_and_swap_cache(struct page *page)
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{
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free_swap_cache(page);
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page_cache_release(page);
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}
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/*
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* Passed an array of pages, drop them all from swapcache and then release
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* them. They are removed from the LRU and freed if this is their last use.
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*/
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void free_pages_and_swap_cache(struct page **pages, int nr)
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{
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struct page **pagep = pages;
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lru_add_drain();
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while (nr) {
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int todo = min(nr, PAGEVEC_SIZE);
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int i;
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for (i = 0; i < todo; i++)
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free_swap_cache(pagep[i]);
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release_pages(pagep, todo, 0);
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pagep += todo;
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nr -= todo;
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}
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}
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/*
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* Lookup a swap entry in the swap cache. A found page will be returned
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* unlocked and with its refcount incremented - we rely on the kernel
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* lock getting page table operations atomic even if we drop the page
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* lock before returning.
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*/
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struct page * lookup_swap_cache(swp_entry_t entry)
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{
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struct page *page;
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page = find_get_page(&swapper_space, entry.val);
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if (page)
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INC_CACHE_INFO(find_success);
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INC_CACHE_INFO(find_total);
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return page;
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}
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/*
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* Locate a page of swap in physical memory, reserving swap cache space
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* and reading the disk if it is not already cached.
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* A failure return means that either the page allocation failed or that
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* the swap entry is no longer in use.
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*/
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struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
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struct vm_area_struct *vma, unsigned long addr)
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{
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struct page *found_page, *new_page = NULL;
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int err;
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do {
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/*
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* First check the swap cache. Since this is normally
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* called after lookup_swap_cache() failed, re-calling
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* that would confuse statistics.
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*/
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found_page = find_get_page(&swapper_space, entry.val);
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if (found_page)
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break;
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/*
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* Get a new page to read into from swap.
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*/
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if (!new_page) {
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new_page = alloc_page_vma(gfp_mask, vma, addr);
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if (!new_page)
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break; /* Out of memory */
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}
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/*
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* call radix_tree_preload() while we can wait.
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*/
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err = radix_tree_preload(gfp_mask & GFP_KERNEL);
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if (err)
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break;
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/*
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* Swap entry may have been freed since our caller observed it.
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*/
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err = swapcache_prepare(entry);
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if (err == -EEXIST) { /* seems racy */
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radix_tree_preload_end();
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continue;
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}
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if (err) { /* swp entry is obsolete ? */
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radix_tree_preload_end();
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break;
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}
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/* May fail (-ENOMEM) if radix-tree node allocation failed. */
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__set_page_locked(new_page);
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SetPageSwapBacked(new_page);
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err = __add_to_swap_cache(new_page, entry);
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if (likely(!err)) {
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radix_tree_preload_end();
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/*
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* Initiate read into locked page and return.
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*/
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lru_cache_add_anon(new_page);
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swap_readpage(new_page);
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return new_page;
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}
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radix_tree_preload_end();
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ClearPageSwapBacked(new_page);
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__clear_page_locked(new_page);
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/*
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* add_to_swap_cache() doesn't return -EEXIST, so we can safely
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* clear SWAP_HAS_CACHE flag.
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*/
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swapcache_free(entry, NULL);
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} while (err != -ENOMEM);
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if (new_page)
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page_cache_release(new_page);
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return found_page;
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}
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/**
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* swapin_readahead - swap in pages in hope we need them soon
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* @entry: swap entry of this memory
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* @gfp_mask: memory allocation flags
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* @vma: user vma this address belongs to
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* @addr: target address for mempolicy
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*
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* Returns the struct page for entry and addr, after queueing swapin.
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*
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* Primitive swap readahead code. We simply read an aligned block of
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* (1 << page_cluster) entries in the swap area. This method is chosen
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* because it doesn't cost us any seek time. We also make sure to queue
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* the 'original' request together with the readahead ones...
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*
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* This has been extended to use the NUMA policies from the mm triggering
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* the readahead.
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*
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* Caller must hold down_read on the vma->vm_mm if vma is not NULL.
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*/
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struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
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struct vm_area_struct *vma, unsigned long addr)
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{
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struct page *page;
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unsigned long offset = swp_offset(entry);
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unsigned long start_offset, end_offset;
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unsigned long mask = (1UL << page_cluster) - 1;
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struct blk_plug plug;
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/* Read a page_cluster sized and aligned cluster around offset. */
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start_offset = offset & ~mask;
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end_offset = offset | mask;
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if (!start_offset) /* First page is swap header. */
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start_offset++;
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blk_start_plug(&plug);
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for (offset = start_offset; offset <= end_offset ; offset++) {
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/* Ok, do the async read-ahead now */
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page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
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gfp_mask, vma, addr);
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if (!page)
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continue;
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page_cache_release(page);
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}
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blk_finish_plug(&plug);
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lru_add_drain(); /* Push any new pages onto the LRU now */
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return read_swap_cache_async(entry, gfp_mask, vma, addr);
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}
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