On Thu, 5 Jul 2012, Johannes Weiner wrote:
> Once charged, swapcache pages can only be uncharged after they are
> removed from swapcache again.
>
> Do not try to uncharge pages that are known to be in the swapcache, to
> allow future patches to remove checks for that in the uncharge code.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> mm/shmem.c | 11 ++++++-----
> 1 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index ee1c5a2..d12b705 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -302,8 +302,6 @@ static int shmem_add_to_page_cache(struct page *page,
> if (!expected)
> radix_tree_preload_end();
> }
> - if (error)
> - mem_cgroup_uncharge_cache_page(page);
> return error;
> }
>
> @@ -1184,11 +1182,14 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
> __set_page_locked(page);
> error = mem_cgroup_cache_charge(page, current->mm,
> gfp & GFP_RECLAIM_MASK);
> - if (!error)
> - error = shmem_add_to_page_cache(page, mapping, index,
> - gfp, NULL);
> if (error)
> goto decused;
> + error = shmem_add_to_page_cache(page, mapping, index,
> + gfp, NULL);
> + if (error) {
> + mem_cgroup_uncharge_cache_page(page);
> + goto decused;
> + }
> lru_cache_add_anon(page);
>
> spin_lock(&info->lock);
> --
I wanted to try this series out on mmotm before replying, and that
took a while; but the problems (some experimental RCU stuff, since
reverted; and Michal's wait_on_page_writeback in vmscan.c, I'll have
to investigate that later) were in mmotm rather than your series:
seems to be running fine under load now.
I've not reviewed, but definitely approve avoiding the temporary
extra charge in migration, and your other simplifications.
And I do approve this change, but selfishly withhold my Ack because
it's a subset of small shmem.c changes I was already lining up to
post, hoping still to sneak into 3.5. We have a real bug in there
(charging to wrong memcg), and this cleanup comes along with that.
I'll post my version in an hour or two.
Hugh
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