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Commit 7e924aaf authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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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: default avatarHugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Acked-by: default avatarBalbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: default avatarKAMEZAWA 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9442ec9d

mm/memcontrol.c

+21 −40
Original line number Diff line number Diff line
@@ -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,
@@ -585,7 +566,6 @@ 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);

	/*
@@ -604,7 +584,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm, 
		}

	}

	unlock_page_cgroup(page);

	}



	pc = kzalloc(sizeof(struct page_cgroup), gfp_mask);

	if (pc == NULL)
@@ -663,7 +642,9 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm, 
	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 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm, 
		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);

mm/shmem.c

+6 −3
Original line number Diff line number Diff line
@@ -1370,14 +1370,17 @@ static int shmem_getpage(struct inode *inode, unsigned long idx, 
			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) {