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mm: munlock: batch non-THP page isolation and munlock+putback using pagevec 

Currently, munlock_vma_range() calls munlock_vma_page on each page in a
loop, which results in repeated taking and releasing of the lru_lock
spinlock for isolating pages one by one.  This patch batches the munlock
operations using an on-stack pagevec, so that isolation is done under
single lru_lock.  For THP pages, the old behavior is preserved as they
might be split while putting them into the pagevec.  After this patch, a
9% speedup was measured for munlocking a 56GB large memory area with THP
disabled.

A new function __munlock_pagevec() is introduced that takes a pagevec and:
1) It clears PageMlocked and isolates all pages under lru_lock.  Zone page
stats can be also updated using the variant which assumes disabled
interrupts.  2) It finishes the munlock and lru putback on all pages under
their lock_page.  Note that previously, lock_page covered also the
PageMlocked clearing and page isolation, but it is not needed for those
operations.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Jörn Engel <joern@logfs.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vlastimil Babka 2013-09-11 14:22:29 -07:00 committed by Linus Torvalds
parent 586a32ac1d
commit 7225522bb4
1 changed files with 156 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

196
mm/mlock.c
View File

@ -11,6 +11,7 @@
#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>
@ -18,6 +19,8 @@
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>
#include <linux/memcontrol.h>
#include <linux/mm_inline.h>
#include "internal.h"
@ -87,6 +90,47 @@ void mlock_vma_page(struct page *page)
}
}
/*
* 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
@ -112,37 +156,10 @@ unsigned int munlock_vma_page(struct page *page)
unsigned int nr_pages = hpage_nr_pages(page);
mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
page_mask = nr_pages - 1;
if (!isolate_lru_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);
} else {
/*
* Some other task has 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.
*/
if (PageUnevictable(page))
count_vm_event(UNEVICTABLE_PGSTRANDED);
else
count_vm_event(UNEVICTABLE_PGMUNLOCKED);
}
if (!isolate_lru_page(page))
__munlock_isolated_page(page);
else
__munlock_isolation_failed(page);
}
return page_mask;
@ -209,6 +226,73 @@ static int __mlock_posix_error_return(long retval)
return retval;
}
/*
* 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 pvec is modified during the process. Before returning
* pagevec_reinit() is called on it.
*/
static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
{
int i;
int nr = pagevec_count(pvec);
/* Phase 1: page isolation */
spin_lock_irq(&zone->lru_lock);
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
if (TestClearPageMlocked(page)) {
struct lruvec *lruvec;
int lru;
/* we have disabled interrupts */
__mod_zone_page_state(zone, NR_MLOCK, -1);
if (PageLRU(page)) {
lruvec = mem_cgroup_page_lruvec(page, zone);
lru = page_lru(page);
get_page(page);
ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, lru);
} else {
__munlock_isolation_failed(page);
goto skip_munlock;
}
} else {
skip_munlock:
/*
* We won't be munlocking this page in the next phase
* but we still need to release the follow_page_mask()
* pin.
*/
pvec->pages[i] = NULL;
put_page(page);
}
}
spin_unlock_irq(&zone->lru_lock);
/* Phase 2: page munlock and putback */
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
if (page) {
lock_page(page);
__munlock_isolated_page(page);
unlock_page(page);
put_page(page); /* pin from follow_page_mask() */
}
}
pagevec_reinit(pvec);
}
/*
* munlock_vma_pages_range() - munlock all pages in the vma range.'
* @vma - vma containing range to be munlock()ed.
@ -230,11 +314,16 @@ static int __mlock_posix_error_return(long retval)
void munlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
struct pagevec pvec;
struct zone *zone = NULL;
pagevec_init(&pvec, 0);
vma->vm_flags &= ~VM_LOCKED;
while (start < end) {
struct page *page;
unsigned int page_mask, page_increm;
struct zone *pagezone;
/*
* Although FOLL_DUMP is intended for get_dump_page(),
@ -246,20 +335,47 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
&page_mask);
if (page && !IS_ERR(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);
pagezone = page_zone(page);
/* The whole pagevec must be in the same zone */
if (pagezone != zone) {
if (pagevec_count(&pvec))
__munlock_pagevec(&pvec, zone);
zone = pagezone;
}
if (PageTransHuge(page)) {
/*
* THP pages are not handled by pagevec due
* to their possible split (see below).
*/
if (pagevec_count(&pvec))
__munlock_pagevec(&pvec, zone);
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.
*/
if (pagevec_add(&pvec, page) == 0)
__munlock_pagevec(&pvec, zone);
}
}
page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
start += page_increm * PAGE_SIZE;
cond_resched();
}
if (pagevec_count(&pvec))
__munlock_pagevec(&pvec, zone);
}
/*