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Date: Wed, 16 Jul 2014 10:14:47 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: Michal Hocko <mhocko@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>, Tejun Heo <tj@...nel.org>,
Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 13/13] mm: memcontrol: rewrite uncharge API
On Wed, Jul 16, 2014 at 09:30:50AM -0400, Naoya Horiguchi wrote:
> On Tue, Jul 15, 2014 at 05:48:43PM -0400, Johannes Weiner wrote:
> > On Tue, Jul 15, 2014 at 04:49:53PM -0400, Naoya Horiguchi wrote:
> > > I feel that these 2 messages have the same cause (just appear differently).
> > > __add_to_page_cache_locked() (and mem_cgroup_try_charge()) can be called
> > > for hugetlb, while we avoid calling mem_cgroup_migrate()/mem_cgroup_uncharge()
> > > for hugetlb. This seems to make page_cgroup of the hugepage inconsistent,
> > > and results in the bad page bug ("page dumped because: cgroup check failed").
> > > So maybe some more PageHuge check is necessary around the charging code.
> >
> > This struck me as odd because I don't remember removing a PageHuge()
> > call in the charge path and wondered how it worked before my changes:
> > apparently it just checked PageCompound() in mem_cgroup_charge_file().
> >
> > So it's not fallout of the new uncharge batching code, but was already
> > broken during the rewrite of the charge API because then hugetlb pages
> > entered the charging code.
> >
> > Anyway, we don't have file-specific charging code anymore, and the
> > PageCompound() check would have required changing anyway for THP
> > cache. So I guess the solution is checking PageHuge() in charge,
> > uncharge, and migrate for now. Oh well.
> >
> > How about this?
>
> With tweaking a bit, this patch solved the problem, thanks!
>
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 9c99d6868a5e..b61194273b56 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -564,9 +564,12 @@ static int __add_to_page_cache_locked(struct page *page,
> > VM_BUG_ON_PAGE(!PageLocked(page), page);
> > VM_BUG_ON_PAGE(PageSwapBacked(page), page);
> >
> > - error = mem_cgroup_try_charge(page, current->mm, gfp_mask, &memcg);
> > - if (error)
> > - return error;
> > + if (!PageHuge(page)) {
> > + error = mem_cgroup_try_charge(page, current->mm,
> > + gfp_mask, &memcg);
> > + if (error)
> > + return error;
> > + }
> >
> > error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
> > if (error) {
>
> We have mem_cgroup_commit_charge() later in __add_to_page_cache_locked(),
> so adding "if (!PageHuge(page))" for it is necessary too.
You are right. Annotated them all now.
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 7f5a42403fae..dabed2f08609 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -781,7 +781,8 @@ static int move_to_new_page(struct page *newpage, struct page *page,
> > if (!PageAnon(newpage))
> > newpage->mapping = NULL;
> > } else {
> > - mem_cgroup_migrate(page, newpage, false);
> > + if (!PageHuge(page))
> > + mem_cgroup_migrate(page, newpage, false);
I deleted this again as it was a followup fix to hugepages getting
wrongfully charged as file cache. They shouldn't be, and
mem_cgroup_migrate() checks whether the page is charged.
> > if (remap_swapcache)
> > remove_migration_ptes(page, newpage);
> > if (!PageAnon(page))
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 3461f2f5be20..97b6ec132398 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -62,12 +62,12 @@ static void __page_cache_release(struct page *page)
> > del_page_from_lru_list(page, lruvec, page_off_lru(page));
> > spin_unlock_irqrestore(&zone->lru_lock, flags);
> > }
> > - mem_cgroup_uncharge(page);
> > }
> >
> > static void __put_single_page(struct page *page)
> > {
> > __page_cache_release(page);
> > + mem_cgroup_uncharge_page(page);
>
> My kernel is based on mmotm-2014-07-09-17-08, where mem_cgroup_uncharge_page()
> does not exist any more. Maybe mem_cgroup_uncharge(page) seems correct.
Sorry, I should have build tested. The name is still reflex...
> > free_hot_cold_page(page, false);
> > }
> >
> > @@ -75,7 +75,10 @@ static void __put_compound_page(struct page *page)
> > {
> > compound_page_dtor *dtor;
> >
> > - __page_cache_release(page);
> > + if (!PageHuge(page)) {
> > + __page_cache_release(page);
> > + mem_cgroup_uncharge_page(page);
I reverted all these mm/swap.c changes again as well. Instead,
mem_cgroup_uncharge() now does a preliminary check if the page is
charged before it touches page->lru.
That should be much more robust: now the vetting whether a page is
valid for memcg happens at charge time only, all other operations
check first if a page is charged before doing anything else to it.
These two places should be the only ones that need fixing then:
diff --git a/mm/filemap.c b/mm/filemap.c
index 9c99d6868a5e..bfe0745a704d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -31,6 +31,7 @@
#include <linux/security.h>
#include <linux/cpuset.h>
#include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
+#include <linux/hugetlb.h>
#include <linux/memcontrol.h>
#include <linux/cleancache.h>
#include <linux/rmap.h>
@@ -558,19 +559,24 @@ static int __add_to_page_cache_locked(struct page *page,
pgoff_t offset, gfp_t gfp_mask,
void **shadowp)
{
+ int huge = PageHuge(page);
struct mem_cgroup *memcg;
int error;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageSwapBacked(page), page);
- error = mem_cgroup_try_charge(page, current->mm, gfp_mask, &memcg);
- if (error)
- return error;
+ if (!huge) {
+ error = mem_cgroup_try_charge(page, current->mm,
+ gfp_mask, &memcg);
+ if (error)
+ return error;
+ }
error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
if (error) {
- mem_cgroup_cancel_charge(page, memcg);
+ if (!huge)
+ mem_cgroup_cancel_charge(page, memcg);
return error;
}
@@ -585,14 +591,16 @@ static int __add_to_page_cache_locked(struct page *page,
goto err_insert;
__inc_zone_page_state(page, NR_FILE_PAGES);
spin_unlock_irq(&mapping->tree_lock);
- mem_cgroup_commit_charge(page, memcg, false);
+ if (!huge)
+ mem_cgroup_commit_charge(page, memcg, false);
trace_mm_filemap_add_to_page_cache(page);
return 0;
err_insert:
page->mapping = NULL;
/* Leave page->index set: truncation relies upon it */
spin_unlock_irq(&mapping->tree_lock);
- mem_cgroup_cancel_charge(page, memcg);
+ if (!huge)
+ mem_cgroup_cancel_charge(page, memcg);
page_cache_release(page);
return error;
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 063080e35459..b5de5deddbfb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6635,9 +6635,16 @@ static void uncharge_list(struct list_head *page_list)
*/
void mem_cgroup_uncharge(struct page *page)
{
+ struct page_cgroup *pc;
+
if (mem_cgroup_disabled())
return;
+ /* Don't touch page->lru of any random page, pre-check: */
+ pc = lookup_page_cgroup(page);
+ if (!PageCgroupUsed(pc))
+ return;
+
INIT_LIST_HEAD(&page->lru);
uncharge_list(&page->lru);
}
--
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