linux-kernel - Re: [PATCH -mm] memcg: fix handling of shmem migration

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Date:	Wed, 17 Sep 2008 15:19:51 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	nishimura@....nes.nec.co.jp, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org,
	balbir@...ux.vnet.ibm.com, xemul@...nvz.org
Subject: Re: [PATCH -mm] memcg: fix handling of shmem migration

On Wed, 17 Sep 2008 14:50:03 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 17 Sep 2008 14:46:59 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> > On Wed, 17 Sep 2008 13:31:49 +0900
> > Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> > 
> > > PG_swapbacked flag of newpage should be set(if needed) before
> > > mem_cgroup_prepare_migration, because mem_cgroup_charge_common
> > > checks the flag and determines whether it sets PAGE_CGROUP_FLAG_FILE or not.
> > > 
> > > Before this patch, if migrating shmem/tmpfs pages, newpage would be
> > > charged with PAGE_CGROUP_FLAG_FILE set, while oldpage has been charged
> > > without the flag.
> > > 
> > Nice catch !
> > Thank you. 
> > 
> > Hmm, should I add MEM_CGROUP_CHARGE_TYPE_SHMEM rather than
> > setting flag to newpage ?
> > 
> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> I acked but.. can't this change moved into memcontrol.c ?
> 

Hmm, something like this?

---
@@ -734,6 +734,9 @@ int mem_cgroup_prepare_migration(struct page *page, struct page *newpa
        if (mem_cgroup_subsys.disabled)
                return 0;

+       if (PageSwapBacked(page))
+               SetPageSwapBacked(newpage);
+
        lock_page_cgroup(page);
        pc = page_get_page_cgroup(page);
        if (pc) {
---

Or, adding MEM_CGROUP_CHARGE_TYPE_SHMEM and

---
@@ -740,7 +740,10 @@ int mem_cgroup_prepare_migration(struct page *page, struct page *newp
                mem = pc->mem_cgroup;
                css_get(&mem->css);
                if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
-                       ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
+                       if (page_is_file_cache(page))
+                               ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
+                       else
+                               ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
        }
        unlock_page_cgroup(page);
        if (mem) {
---
(Of course, mem_cgroup_charge_common should be modified too.)


Thanks,
Daisuke Nishimura.
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