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/*
* 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)
{
unsigned 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);
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);
__munlock_isolated_page(page);
goto out;
}
__munlock_isolation_failed(page);
unlock_out:
spin_unlock_irq(&zone->lru_lock);
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(
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