linux/mm/mlock.c
Mel Gorman a52633d8e9 mm, vmscan: move lru_lock to the node
Node-based reclaim requires node-based LRUs and locking.  This is a
preparation patch that just moves the lru_lock to the node so later
patches are easier to review.  It is a mechanical change but note this
patch makes contention worse because the LRU lock is hotter and direct
reclaim and kswapd can contend on the same lock even when reclaiming
from different zones.

Link: http://lkml.kernel.org/r/1467970510-21195-3-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-07-28 16:07:41 -07:00

813 lines
21 KiB
C

/*
* linux/mm/mlock.c
*
* (C) Copyright 1995 Linus Torvalds
* (C) Copyright 2002 Christoph Hellwig
*/
#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>
#include <linux/memcontrol.h>
#include <linux/mm_inline.h>
#include "internal.h"
bool can_do_mlock(void)
{
if (rlimit(RLIMIT_MEMLOCK) != 0)
return true;
if (capable(CAP_IPC_LOCK))
return true;
return false;
}
EXPORT_SYMBOL(can_do_mlock);
/*
* Mlocked pages are marked with PageMlocked() flag for efficient testing
* in vmscan and, possibly, the fault path; and to support semi-accurate
* statistics.
*
* An mlocked page [PageMlocked(page)] is unevictable. As such, it will
* be placed on the LRU "unevictable" list, rather than the [in]active lists.
* The unevictable list is an LRU sibling list to the [in]active lists.
* PageUnevictable is set to indicate the unevictable state.
*
* When lazy mlocking via vmscan, it is important to ensure that the
* vma's VM_LOCKED status is not concurrently being modified, otherwise we
* may have mlocked a page that is being munlocked. So lazy mlock must take
* the mmap_sem for read, and verify that the vma really is locked
* (see mm/rmap.c).
*/
/*
* LRU accounting for clear_page_mlock()
*/
void clear_page_mlock(struct page *page)
{
if (!TestClearPageMlocked(page))
return;
mod_zone_page_state(page_zone(page), NR_MLOCK,
-hpage_nr_pages(page));
count_vm_event(UNEVICTABLE_PGCLEARED);
if (!isolate_lru_page(page)) {
putback_lru_page(page);
} else {
/*
* We lost the race. the page already moved to evictable list.
*/
if (PageUnevictable(page))
count_vm_event(UNEVICTABLE_PGSTRANDED);
}
}
/*
* Mark page as mlocked if not already.
* If page on LRU, isolate and putback to move to unevictable list.
*/
void mlock_vma_page(struct page *page)
{
/* Serialize with page migration */
BUG_ON(!PageLocked(page));
VM_BUG_ON_PAGE(PageTail(page), page);
VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
if (!TestSetPageMlocked(page)) {
mod_zone_page_state(page_zone(page), NR_MLOCK,
hpage_nr_pages(page));
count_vm_event(UNEVICTABLE_PGMLOCKED);
if (!isolate_lru_page(page))
putback_lru_page(page);
}
}
/*
* Isolate a page from LRU with optional get_page() pin.
* Assumes lru_lock already held and page already pinned.
*/
static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
{
if (PageLRU(page)) {
struct lruvec *lruvec;
lruvec = mem_cgroup_page_lruvec(page, page_zone(page));
if (getpage)
get_page(page);
ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, page_lru(page));
return true;
}
return false;
}
/*
* Finish munlock after successful page isolation
*
* Page must be locked. This is a wrapper for try_to_munlock()
* and putback_lru_page() with munlock accounting.
*/
static void __munlock_isolated_page(struct page *page)
{
int ret = SWAP_AGAIN;
/*
* Optimization: if the page was mapped just once, that's our mapping
* and we don't need to check all the other vmas.
*/
if (page_mapcount(page) > 1)
ret = try_to_munlock(page);
/* Did try_to_unlock() succeed or punt? */
if (ret != SWAP_MLOCK)
count_vm_event(UNEVICTABLE_PGMUNLOCKED);
putback_lru_page(page);
}
/*
* Accounting for page isolation fail during munlock
*
* Performs accounting when page isolation fails in munlock. There is nothing
* else to do because it means some other task has already removed the page
* from the LRU. putback_lru_page() will take care of removing the page from
* the unevictable list, if necessary. vmscan [page_referenced()] will move
* the page back to the unevictable list if some other vma has it mlocked.
*/
static void __munlock_isolation_failed(struct page *page)
{
if (PageUnevictable(page))
__count_vm_event(UNEVICTABLE_PGSTRANDED);
else
__count_vm_event(UNEVICTABLE_PGMUNLOCKED);
}
/**
* munlock_vma_page - munlock a vma page
* @page - page to be unlocked, either a normal page or THP page head
*
* returns the size of the page as a page mask (0 for normal page,
* HPAGE_PMD_NR - 1 for THP head page)
*
* called from munlock()/munmap() path with page supposedly on the LRU.
* When we munlock a page, because the vma where we found the page is being
* munlock()ed or munmap()ed, we want to check whether other vmas hold the
* page locked so that we can leave it on the unevictable lru list and not
* bother vmscan with it. However, to walk the page's rmap list in
* try_to_munlock() we must isolate the page from the LRU. If some other
* task has removed the page from the LRU, we won't be able to do that.
* So we clear the PageMlocked as we might not get another chance. If we
* can't isolate the page, we leave it for putback_lru_page() and vmscan
* [page_referenced()/try_to_unmap()] to deal with.
*/
unsigned int munlock_vma_page(struct page *page)
{
int nr_pages;
struct zone *zone = page_zone(page);
/* For try_to_munlock() and to serialize with page migration */
BUG_ON(!PageLocked(page));
VM_BUG_ON_PAGE(PageTail(page), page);
/*
* Serialize with any parallel __split_huge_page_refcount() which
* might otherwise copy PageMlocked to part of the tail pages before
* we clear it in the head page. It also stabilizes hpage_nr_pages().
*/
spin_lock_irq(zone_lru_lock(zone));
nr_pages = hpage_nr_pages(page);
if (!TestClearPageMlocked(page))
goto unlock_out;
__mod_zone_page_state(zone, NR_MLOCK, -nr_pages);
if (__munlock_isolate_lru_page(page, true)) {
spin_unlock_irq(zone_lru_lock(zone));
__munlock_isolated_page(page);
goto out;
}
__munlock_isolation_failed(page);
unlock_out:
spin_unlock_irq(zone_lru_lock(zone));
out:
return nr_pages - 1;
}
/*
* convert get_user_pages() return value to posix mlock() error
*/
static int __mlock_posix_error_return(long retval)
{
if (retval == -EFAULT)
retval = -ENOMEM;
else if (retval == -ENOMEM)
retval = -EAGAIN;
return retval;
}
/*
* Prepare page for fast batched LRU putback via putback_lru_evictable_pagevec()
*
* The fast path is available only for evictable pages with single mapping.
* Then we can bypass the per-cpu pvec and get better performance.
* when mapcount > 1 we need try_to_munlock() which can fail.
* when !page_evictable(), we need the full redo logic of putback_lru_page to
* avoid leaving evictable page in unevictable list.
*
* In case of success, @page is added to @pvec and @pgrescued is incremented
* in case that the page was previously unevictable. @page is also unlocked.
*/
static bool __putback_lru_fast_prepare(struct page *page, struct pagevec *pvec,
int *pgrescued)
{
VM_BUG_ON_PAGE(PageLRU(page), page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
if (page_mapcount(page) <= 1 && page_evictable(page)) {
pagevec_add(pvec, page);
if (TestClearPageUnevictable(page))
(*pgrescued)++;
unlock_page(page);
return true;
}
return false;
}
/*
* Putback multiple evictable pages to the LRU
*
* Batched putback of evictable pages that bypasses the per-cpu pvec. Some of
* the pages might have meanwhile become unevictable but that is OK.
*/
static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
{
count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));
/*
*__pagevec_lru_add() calls release_pages() so we don't call
* put_page() explicitly
*/
__pagevec_lru_add(pvec);
count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
}
/*
* Munlock a batch of pages from the same zone
*
* The work is split to two main phases. First phase clears the Mlocked flag
* and attempts to isolate the pages, all under a single zone lru lock.
* The second phase finishes the munlock only for pages where isolation
* succeeded.
*
* Note that the pagevec may be modified during the process.
*/
static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
{
int i;
int nr = pagevec_count(pvec);
int delta_munlocked;
struct pagevec pvec_putback;
int pgrescued = 0;
pagevec_init(&pvec_putback, 0);
/* Phase 1: page isolation */
spin_lock_irq(zone_lru_lock(zone));
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
if (TestClearPageMlocked(page)) {
/*
* We already have pin from follow_page_mask()
* so we can spare the get_page() here.
*/
if (__munlock_isolate_lru_page(page, false))
continue;
else
__munlock_isolation_failed(page);
}
/*
* We won't be munlocking this page in the next phase
* but we still need to release the follow_page_mask()
* pin. We cannot do it under lru_lock however. If it's
* the last pin, __page_cache_release() would deadlock.
*/
pagevec_add(&pvec_putback, pvec->pages[i]);
pvec->pages[i] = NULL;
}
delta_munlocked = -nr + pagevec_count(&pvec_putback);
__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
spin_unlock_irq(zone_lru_lock(zone));
/* Now we can release pins of pages that we are not munlocking */
pagevec_release(&pvec_putback);
/* Phase 2: page munlock */
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
if (page) {
lock_page(page);
if (!__putback_lru_fast_prepare(page, &pvec_putback,
&pgrescued)) {
/*
* Slow path. We don't want to lose the last
* pin before unlock_page()
*/
get_page(page); /* for putback_lru_page() */
__munlock_isolated_page(page);
unlock_page(page);
put_page(page); /* from follow_page_mask() */
}
}
}
/*
* Phase 3: page putback for pages that qualified for the fast path
* This will also call put_page() to return pin from follow_page_mask()
*/
if (pagevec_count(&pvec_putback))
__putback_lru_fast(&pvec_putback, pgrescued);
}
/*
* Fill up pagevec for __munlock_pagevec using pte walk
*
* The function expects that the struct page corresponding to @start address is
* a non-TPH page already pinned and in the @pvec, and that it belongs to @zone.
*
* The rest of @pvec is filled by subsequent pages within the same pmd and same
* zone, as long as the pte's are present and vm_normal_page() succeeds. These
* pages also get pinned.
*
* Returns the address of the next page that should be scanned. This equals
* @start + PAGE_SIZE when no page could be added by the pte walk.
*/
static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
struct vm_area_struct *vma, int zoneid, unsigned long start,
unsigned long end)
{
pte_t *pte;
spinlock_t *ptl;
/*
* Initialize pte walk starting at the already pinned page where we
* are sure that there is a pte, as it was pinned under the same
* mmap_sem write op.
*/
pte = get_locked_pte(vma->vm_mm, start, &ptl);
/* Make sure we do not cross the page table boundary */
end = pgd_addr_end(start, end);
end = pud_addr_end(start, end);
end = pmd_addr_end(start, end);
/* The page next to the pinned page is the first we will try to get */
start += PAGE_SIZE;
while (start < end) {
struct page *page = NULL;
pte++;
if (pte_present(*pte))
page = vm_normal_page(vma, start, *pte);
/*
* Break if page could not be obtained or the page's node+zone does not
* match
*/
if (!page || page_zone_id(page) != zoneid)
break;
/*
* Do not use pagevec for PTE-mapped THP,
* munlock_vma_pages_range() will handle them.
*/
if (PageTransCompound(page))
break;
get_page(page);
/*
* Increase the address that will be returned *before* the
* eventual break due to pvec becoming full by adding the page
*/
start += PAGE_SIZE;
if (pagevec_add(pvec, page) == 0)
break;
}
pte_unmap_unlock(pte, ptl);
return start;
}
/*
* munlock_vma_pages_range() - munlock all pages in the vma range.'
* @vma - vma containing range to be munlock()ed.
* @start - start address in @vma of the range
* @end - end of range in @vma.
*
* For mremap(), munmap() and exit().
*
* Called with @vma VM_LOCKED.
*
* Returns with VM_LOCKED cleared. Callers must be prepared to
* deal with this.
*
* We don't save and restore VM_LOCKED here because pages are
* still on lru. In unmap path, pages might be scanned by reclaim
* and re-mlocked by try_to_{munlock|unmap} before we unmap and
* free them. This will result in freeing mlocked pages.
*/
void munlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
while (start < end) {
struct page *page;
unsigned int page_mask;
unsigned long page_increm;
struct pagevec pvec;
struct zone *zone;
int zoneid;
pagevec_init(&pvec, 0);
/*
* Although FOLL_DUMP is intended for get_dump_page(),
* it just so happens that its special treatment of the
* ZERO_PAGE (returning an error instead of doing get_page)
* suits munlock very well (and if somehow an abnormal page
* has sneaked into the range, we won't oops here: great).
*/
page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
&page_mask);
if (page && !IS_ERR(page)) {
if (PageTransTail(page)) {
VM_BUG_ON_PAGE(PageMlocked(page), page);
put_page(page); /* follow_page_mask() */
} else if (PageTransHuge(page)) {
lock_page(page);
/*
* Any THP page found by follow_page_mask() may
* have gotten split before reaching
* munlock_vma_page(), so we need to recompute
* the page_mask here.
*/
page_mask = munlock_vma_page(page);
unlock_page(page);
put_page(page); /* follow_page_mask() */
} else {
/*
* Non-huge pages are handled in batches via
* pagevec. The pin from follow_page_mask()
* prevents them from collapsing by THP.
*/
pagevec_add(&pvec, page);
zone = page_zone(page);
zoneid = page_zone_id(page);
/*
* Try to fill the rest of pagevec using fast
* pte walk. This will also update start to
* the next page to process. Then munlock the
* pagevec.
*/
start = __munlock_pagevec_fill(&pvec, vma,
zoneid, start, end);
__munlock_pagevec(&pvec, zone);
goto next;
}
}
page_increm = 1 + page_mask;
start += page_increm * PAGE_SIZE;
next:
cond_resched();
}
}
/*
* mlock_fixup - handle mlock[all]/munlock[all] requests.
*
* Filters out "special" vmas -- VM_LOCKED never gets set for these, and
* munlock is a no-op. However, for some special vmas, we go ahead and
* populate the ptes.
*
* For vmas that pass the filters, merge/split as appropriate.
*/
static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
unsigned long start, unsigned long end, vm_flags_t newflags)
{
struct mm_struct *mm = vma->vm_mm;
pgoff_t pgoff;
int nr_pages;
int ret = 0;
int lock = !!(newflags & VM_LOCKED);
if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
/* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
goto out;
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
vma->vm_file, pgoff, vma_policy(vma),
vma->vm_userfaultfd_ctx);
if (*prev) {
vma = *prev;
goto success;
}
if (start != vma->vm_start) {
ret = split_vma(mm, vma, start, 1);
if (ret)
goto out;
}
if (end != vma->vm_end) {
ret = split_vma(mm, vma, end, 0);
if (ret)
goto out;
}
success:
/*
* Keep track of amount of locked VM.
*/
nr_pages = (end - start) >> PAGE_SHIFT;
if (!lock)
nr_pages = -nr_pages;
mm->locked_vm += nr_pages;
/*
* vm_flags is protected by the mmap_sem held in write mode.
* It's okay if try_to_unmap_one unmaps a page just after we
* set VM_LOCKED, populate_vma_page_range will bring it back.
*/
if (lock)
vma->vm_flags = newflags;
else
munlock_vma_pages_range(vma, start, end);
out:
*prev = vma;
return ret;
}
static int apply_vma_lock_flags(unsigned long start, size_t len,
vm_flags_t flags)
{
unsigned long nstart, end, tmp;
struct vm_area_struct * vma, * prev;
int error;
VM_BUG_ON(offset_in_page(start));
VM_BUG_ON(len != PAGE_ALIGN(len));
end = start + len;
if (end < start)
return -EINVAL;
if (end == start)
return 0;
vma = find_vma(current->mm, start);
if (!vma || vma->vm_start > start)
return -ENOMEM;
prev = vma->vm_prev;
if (start > vma->vm_start)
prev = vma;
for (nstart = start ; ; ) {
vm_flags_t newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
newflags |= flags;
/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
tmp = vma->vm_end;
if (tmp > end)
tmp = end;
error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
if (error)
break;
nstart = tmp;
if (nstart < prev->vm_end)
nstart = prev->vm_end;
if (nstart >= end)
break;
vma = prev->vm_next;
if (!vma || vma->vm_start != nstart) {
error = -ENOMEM;
break;
}
}
return error;
}
static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t flags)
{
unsigned long locked;
unsigned long lock_limit;
int error = -ENOMEM;
if (!can_do_mlock())
return -EPERM;
lru_add_drain_all(); /* flush pagevec */
len = PAGE_ALIGN(len + (offset_in_page(start)));
start &= PAGE_MASK;
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
locked = len >> PAGE_SHIFT;
if (down_write_killable(&current->mm->mmap_sem))
return -EINTR;
locked += current->mm->locked_vm;
/* check against resource limits */
if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
error = apply_vma_lock_flags(start, len, flags);
up_write(&current->mm->mmap_sem);
if (error)
return error;
error = __mm_populate(start, len, 0);
if (error)
return __mlock_posix_error_return(error);
return 0;
}
SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
{
return do_mlock(start, len, VM_LOCKED);
}
SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
{
vm_flags_t vm_flags = VM_LOCKED;
if (flags & ~MLOCK_ONFAULT)
return -EINVAL;
if (flags & MLOCK_ONFAULT)
vm_flags |= VM_LOCKONFAULT;
return do_mlock(start, len, vm_flags);
}
SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
{
int ret;
len = PAGE_ALIGN(len + (offset_in_page(start)));
start &= PAGE_MASK;
if (down_write_killable(&current->mm->mmap_sem))
return -EINTR;
ret = apply_vma_lock_flags(start, len, 0);
up_write(&current->mm->mmap_sem);
return ret;
}
/*
* Take the MCL_* flags passed into mlockall (or 0 if called from munlockall)
* and translate into the appropriate modifications to mm->def_flags and/or the
* flags for all current VMAs.
*
* There are a couple of subtleties with this. If mlockall() is called multiple
* times with different flags, the values do not necessarily stack. If mlockall
* is called once including the MCL_FUTURE flag and then a second time without
* it, VM_LOCKED and VM_LOCKONFAULT will be cleared from mm->def_flags.
*/
static int apply_mlockall_flags(int flags)
{
struct vm_area_struct * vma, * prev = NULL;
vm_flags_t to_add = 0;
current->mm->def_flags &= VM_LOCKED_CLEAR_MASK;
if (flags & MCL_FUTURE) {
current->mm->def_flags |= VM_LOCKED;
if (flags & MCL_ONFAULT)
current->mm->def_flags |= VM_LOCKONFAULT;
if (!(flags & MCL_CURRENT))
goto out;
}
if (flags & MCL_CURRENT) {
to_add |= VM_LOCKED;
if (flags & MCL_ONFAULT)
to_add |= VM_LOCKONFAULT;
}
for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
vm_flags_t newflags;
newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
newflags |= to_add;
/* Ignore errors */
mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
cond_resched_rcu_qs();
}
out:
return 0;
}
SYSCALL_DEFINE1(mlockall, int, flags)
{
unsigned long lock_limit;
int ret;
if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)))
return -EINVAL;
if (!can_do_mlock())
return -EPERM;
if (flags & MCL_CURRENT)
lru_add_drain_all(); /* flush pagevec */
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
if (down_write_killable(&current->mm->mmap_sem))
return -EINTR;
ret = -ENOMEM;
if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
capable(CAP_IPC_LOCK))
ret = apply_mlockall_flags(flags);
up_write(&current->mm->mmap_sem);
if (!ret && (flags & MCL_CURRENT))
mm_populate(0, TASK_SIZE);
return ret;
}
SYSCALL_DEFINE0(munlockall)
{
int ret;
if (down_write_killable(&current->mm->mmap_sem))
return -EINTR;
ret = apply_mlockall_flags(0);
up_write(&current->mm->mmap_sem);
return ret;
}
/*
* Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
* shm segments) get accounted against the user_struct instead.
*/
static DEFINE_SPINLOCK(shmlock_user_lock);
int user_shm_lock(size_t size, struct user_struct *user)
{
unsigned long lock_limit, locked;
int allowed = 0;
locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
lock_limit = rlimit(RLIMIT_MEMLOCK);
if (lock_limit == RLIM_INFINITY)
allowed = 1;
lock_limit >>= PAGE_SHIFT;
spin_lock(&shmlock_user_lock);
if (!allowed &&
locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
goto out;
get_uid(user);
user->locked_shm += locked;
allowed = 1;
out:
spin_unlock(&shmlock_user_lock);
return allowed;
}
void user_shm_unlock(size_t size, struct user_struct *user)
{
spin_lock(&shmlock_user_lock);
user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
spin_unlock(&shmlock_user_lock);
free_uid(user);
}