Re: [PATCH -mmotm 7/8] memcg: move charges of anonymous swap

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Wed, 3 Feb 2010 19:31:27 -0800, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Mon, 21 Dec 2009 14:38:16 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> > This patch is another core part of this move-charge-at-task-migration feature.
> > It enables moving charges of anonymous swaps.
> > 
> > To move the charge of swap, we need to exchange swap_cgroup's record.
> > 
> > In current implementation, swap_cgroup's record is protected by:
> > 
> >   - page lock: if the entry is on swap cache.
> >   - swap_lock: if the entry is not on swap cache.
> > 
> > This works well in usual swap-in/out activity.
> > 
> > But this behavior make the feature of moving swap charge check many conditions
> > to exchange swap_cgroup's record safely.
> > 
> > So I changed modification of swap_cgroup's recored(swap_cgroup_record())
> > to use xchg, and define a new function to cmpxchg swap_cgroup's record.
> > 
> > This patch also enables moving charge of non pte_present but not uncharged swap
> > caches, which can be exist on swap-out path, by getting the target pages via
> > find_get_page() as do_mincore() does.
> > 
> >
> > ...
> >
> > +		else if (is_swap_pte(ptent)) {
> 
> is_swap_pte() isn't implemented for CONFIG_MMU=n, so the build breaks.
Ah, you're right. I'm sorry I don't have any evironment to test !CONFIG_MMU.

Using #ifdef like below would be the simplest fix(SWAP is depend on MMU),
but hmm, #ifdef is ugly.

I'll prepare another fix.

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

build fix in !CONFIG_MMU case.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 mm/memcontrol.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 953b18b..85b48cb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3635,6 +3635,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
 					&mc.to->move_charge_at_immigrate);
 
 	if (!pte_present(ptent)) {
+#ifdef CONFIG_SWAP
 		/* TODO: handle swap of shmes/tmpfs */
 		if (pte_none(ptent) || pte_file(ptent))
 			return 0;
@@ -3644,6 +3645,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
 				return 0;
 			usage_count = mem_cgroup_count_swap_user(ent, &page);
 		}
+#endif
 	} else {
 		page = vm_normal_page(vma, addr, ptent);
 		if (!page || !page_mapped(page))
-- 
1.6.4

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