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![Johannes Weiner](/assets/img/avatar_default.png)
Without swap page tracking, users that are otherwise memory controlled can easily escape their containment and allocate significant amounts of memory that they're not being charged for. That's because swap does readahead, but without the cgroup records of who owned the page at swapout, readahead pages don't get charged until somebody actually faults them into their page table and we can identify an owner task. This can be maliciously exploited with MADV_WILLNEED, which triggers arbitrary readahead allocations without charging the pages. Make swap swap page tracking an integral part of memcg and remove the Kconfig options. In the first place, it was only made configurable to allow users to save some memory. But the overhead of tracking cgroup ownership per swap page is minimal - 2 byte per page, or 512k per 1G of swap, or 0.04%. Saving that at the expense of broken containment semantics is not something we should present as a coequal option. The swapaccount=0 boot option will continue to exist, and it will eliminate the page_counter overhead and hide the swap control files, but it won't disable swap slot ownership tracking. This patch makes sure we always have the cgroup records at swapin time; the next patch will fix the actual bug by charging readahead swap pages at swapin time rather than at fault time. v2: fix double swap charge bug in cgroup1/cgroup2 code gating [hannes@cmpxchg.org: fix crash with cgroup_disable=memory] Link: http://lkml.kernel.org/r/20200521215855.GB815153@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Alex Shi <alex.shi@linux.alibaba.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Balbir Singh <bsingharora@gmail.com> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200508183105.225460-16-hannes@cmpxchg.org Debugged-by: Hugh Dickins <hughd@google.com> Debugged-by: Michal Hocko <mhocko@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
227 lines
5.1 KiB
C
227 lines
5.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/swap_cgroup.h>
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#include <linux/vmalloc.h>
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#include <linux/mm.h>
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#include <linux/swapops.h> /* depends on mm.h include */
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static DEFINE_MUTEX(swap_cgroup_mutex);
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struct swap_cgroup_ctrl {
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struct page **map;
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unsigned long length;
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spinlock_t lock;
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};
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static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
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struct swap_cgroup {
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unsigned short id;
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};
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#define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
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/*
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* SwapCgroup implements "lookup" and "exchange" operations.
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* In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
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* against SwapCache. At swap_free(), this is accessed directly from swap.
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*
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* This means,
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* - we have no race in "exchange" when we're accessed via SwapCache because
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* SwapCache(and its swp_entry) is under lock.
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* - When called via swap_free(), there is no user of this entry and no race.
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* Then, we don't need lock around "exchange".
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*
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* TODO: we can push these buffers out to HIGHMEM.
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*/
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/*
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* allocate buffer for swap_cgroup.
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*/
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static int swap_cgroup_prepare(int type)
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{
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struct page *page;
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struct swap_cgroup_ctrl *ctrl;
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unsigned long idx, max;
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ctrl = &swap_cgroup_ctrl[type];
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for (idx = 0; idx < ctrl->length; idx++) {
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page = alloc_page(GFP_KERNEL | __GFP_ZERO);
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if (!page)
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goto not_enough_page;
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ctrl->map[idx] = page;
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if (!(idx % SWAP_CLUSTER_MAX))
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cond_resched();
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}
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return 0;
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not_enough_page:
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max = idx;
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for (idx = 0; idx < max; idx++)
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__free_page(ctrl->map[idx]);
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return -ENOMEM;
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}
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static struct swap_cgroup *__lookup_swap_cgroup(struct swap_cgroup_ctrl *ctrl,
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pgoff_t offset)
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{
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struct page *mappage;
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struct swap_cgroup *sc;
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mappage = ctrl->map[offset / SC_PER_PAGE];
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sc = page_address(mappage);
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return sc + offset % SC_PER_PAGE;
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}
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static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
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struct swap_cgroup_ctrl **ctrlp)
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{
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pgoff_t offset = swp_offset(ent);
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struct swap_cgroup_ctrl *ctrl;
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ctrl = &swap_cgroup_ctrl[swp_type(ent)];
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if (ctrlp)
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*ctrlp = ctrl;
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return __lookup_swap_cgroup(ctrl, offset);
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}
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/**
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* swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
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* @ent: swap entry to be cmpxchged
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* @old: old id
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* @new: new id
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*
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* Returns old id at success, 0 at failure.
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* (There is no mem_cgroup using 0 as its id)
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*/
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unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
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unsigned short old, unsigned short new)
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{
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struct swap_cgroup_ctrl *ctrl;
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struct swap_cgroup *sc;
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unsigned long flags;
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unsigned short retval;
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sc = lookup_swap_cgroup(ent, &ctrl);
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spin_lock_irqsave(&ctrl->lock, flags);
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retval = sc->id;
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if (retval == old)
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sc->id = new;
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else
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retval = 0;
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spin_unlock_irqrestore(&ctrl->lock, flags);
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return retval;
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}
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/**
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* swap_cgroup_record - record mem_cgroup for a set of swap entries
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* @ent: the first swap entry to be recorded into
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* @id: mem_cgroup to be recorded
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* @nr_ents: number of swap entries to be recorded
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*
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* Returns old value at success, 0 at failure.
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* (Of course, old value can be 0.)
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*/
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unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
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unsigned int nr_ents)
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{
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struct swap_cgroup_ctrl *ctrl;
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struct swap_cgroup *sc;
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unsigned short old;
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unsigned long flags;
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pgoff_t offset = swp_offset(ent);
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pgoff_t end = offset + nr_ents;
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sc = lookup_swap_cgroup(ent, &ctrl);
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spin_lock_irqsave(&ctrl->lock, flags);
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old = sc->id;
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for (;;) {
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VM_BUG_ON(sc->id != old);
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sc->id = id;
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offset++;
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if (offset == end)
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break;
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if (offset % SC_PER_PAGE)
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sc++;
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else
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sc = __lookup_swap_cgroup(ctrl, offset);
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}
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spin_unlock_irqrestore(&ctrl->lock, flags);
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return old;
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}
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/**
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* lookup_swap_cgroup_id - lookup mem_cgroup id tied to swap entry
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* @ent: swap entry to be looked up.
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*
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* Returns ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)
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*/
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unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
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{
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return lookup_swap_cgroup(ent, NULL)->id;
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}
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int swap_cgroup_swapon(int type, unsigned long max_pages)
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{
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void *array;
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unsigned long array_size;
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unsigned long length;
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struct swap_cgroup_ctrl *ctrl;
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length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
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array_size = length * sizeof(void *);
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array = vzalloc(array_size);
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if (!array)
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goto nomem;
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ctrl = &swap_cgroup_ctrl[type];
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mutex_lock(&swap_cgroup_mutex);
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ctrl->length = length;
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ctrl->map = array;
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spin_lock_init(&ctrl->lock);
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if (swap_cgroup_prepare(type)) {
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/* memory shortage */
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ctrl->map = NULL;
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ctrl->length = 0;
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mutex_unlock(&swap_cgroup_mutex);
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vfree(array);
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goto nomem;
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}
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mutex_unlock(&swap_cgroup_mutex);
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return 0;
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nomem:
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pr_info("couldn't allocate enough memory for swap_cgroup\n");
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pr_info("swap_cgroup can be disabled by swapaccount=0 boot option\n");
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return -ENOMEM;
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}
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void swap_cgroup_swapoff(int type)
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{
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struct page **map;
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unsigned long i, length;
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struct swap_cgroup_ctrl *ctrl;
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mutex_lock(&swap_cgroup_mutex);
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ctrl = &swap_cgroup_ctrl[type];
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map = ctrl->map;
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length = ctrl->length;
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ctrl->map = NULL;
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ctrl->length = 0;
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mutex_unlock(&swap_cgroup_mutex);
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if (map) {
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for (i = 0; i < length; i++) {
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struct page *page = map[i];
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if (page)
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__free_page(page);
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if (!(i % SWAP_CLUSTER_MAX))
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cond_resched();
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}
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vfree(map);
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}
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}
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