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memcg: mem_cgroup_charge never NULL 

My memcgroup patch to fix hang with shmem/tmpfs added NULL page handling to
mem_cgroup_charge_common.  It seemed convenient at the time, but hard to
justify now: there's a perfectly appropriate swappage to charge and uncharge
instead, this is not on any hot path through shmem_getpage, and no performance
hit was observed from the slight extra overhead.

So revert that NULL page handling from mem_cgroup_charge_common; and make it
clearer by bringing page_cgroup_assign_new_page_cgroup into its body - that
was a helper I found more of a hindrance to understanding.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2008-03-04 14:29:08 -08:00 committed by Linus Torvalds
parent 9442ec9df4
commit 7e924aafa4
2 changed files with 27 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
mm/memcontrol.c
View File

@ -300,25 +300,6 @@ static void __always_inline unlock_page_cgroup(struct page *page)
bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}
/*
* Tie new page_cgroup to struct page under lock_page_cgroup()
* This can fail if the page has been tied to a page_cgroup.
* If success, returns 0.
*/
static int page_cgroup_assign_new_page_cgroup(struct page *page,
struct page_cgroup *pc)
{
int ret = 0;
lock_page_cgroup(page);
if (!page_get_page_cgroup(page))
page_assign_page_cgroup(page, pc);
else /* A page is tied to other pc. */
ret = 1;
unlock_page_cgroup(page);
return ret;
}
/*
* Clear page->page_cgroup member under lock_page_cgroup().
* If given "pc" value is different from one page->page_cgroup,
@ -585,26 +566,24 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
* with it
*/
retry:
if (page) {
lock_page_cgroup(page);
pc = page_get_page_cgroup(page);
/*
* The page_cgroup exists and
* the page has already been accounted.
*/
if (pc) {
if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
/* this page is under being uncharged ? */
unlock_page_cgroup(page);
cpu_relax();
goto retry;
} else {
unlock_page_cgroup(page);
goto done;
}
lock_page_cgroup(page);
pc = page_get_page_cgroup(page);
/*
* The page_cgroup exists and
* the page has already been accounted.
*/
if (pc) {
if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
/* this page is under being uncharged ? */
unlock_page_cgroup(page);
cpu_relax();
goto retry;
} else {
unlock_page_cgroup(page);
goto done;
}
unlock_page_cgroup(page);
}
unlock_page_cgroup(page);
pc = kzalloc(sizeof(struct page_cgroup), gfp_mask);
if (pc == NULL)
@ -663,7 +642,9 @@ retry:
if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
pc->flags |= PAGE_CGROUP_FLAG_CACHE;
if (!page || page_cgroup_assign_new_page_cgroup(page, pc)) {
lock_page_cgroup(page);
if (page_get_page_cgroup(page)) {
unlock_page_cgroup(page);
/*
* Another charge has been added to this page already.
* We take lock_page_cgroup(page) again and read
@ -672,10 +653,10 @@ retry:
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
kfree(pc);
if (!page)
goto done;
goto retry;
}
page_assign_page_cgroup(page, pc);
unlock_page_cgroup(page);
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);

9
mm/shmem.c
View File

@ -1370,14 +1370,17 @@ repeat:
shmem_swp_unmap(entry);
spin_unlock(&info->lock);
unlock_page(swappage);
page_cache_release(swappage);
if (error == -ENOMEM) {
/* allow reclaim from this memory cgroup */
error = mem_cgroup_cache_charge(NULL,
error = mem_cgroup_cache_charge(swappage,
current->mm, gfp & ~__GFP_HIGHMEM);
if (error)
if (error) {
page_cache_release(swappage);
goto failed;
}
mem_cgroup_uncharge_page(swappage);
}
page_cache_release(swappage);
goto repeat;
}
} else if (sgp == SGP_READ && !filepage) {