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    SubjectRe: [PATCH v2 02/11] memcg: Reclaim when more than one page needed.
    On Thu 09-08-12 17:01:10, Glauber Costa wrote:
    > From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
    >
    > mem_cgroup_do_charge() was written before kmem accounting, and expects
    > three cases: being called for 1 page, being called for a stock of 32
    > pages, or being called for a hugepage. If we call for 2 or 3 pages (and
    > both the stack and several slabs used in process creation are such, at
    > least with the debug options I had), it assumed it's being called for
    > stock and just retried without reclaiming.
    >
    > Fix that by passing down a minsize argument in addition to the csize.
    >
    > And what to do about that (csize == PAGE_SIZE && ret) retry? If it's
    > needed at all (and presumably is since it's there, perhaps to handle
    > races), then it should be extended to more than PAGE_SIZE, yet how far?
    > And should there be a retry count limit, of what? For now retry up to
    > COSTLY_ORDER (as page_alloc.c does) and make sure not to do it if
    > __GFP_NORETRY.
    >
    > [v4: fixed nr pages calculation pointed out by Christoph Lameter ]
    >
    > Signed-off-by: Suleiman Souhlal <suleiman@google.com>
    > Signed-off-by: Glauber Costa <glommer@parallels.com>
    > Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    I am not happy with the min_pages argument but we can do something more
    clever later.

    Acked-by: Michal Hocko <mhocko@suse.cz>

    > ---
    > mm/memcontrol.c | 16 +++++++++-------
    > 1 file changed, 9 insertions(+), 7 deletions(-)
    >
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index bc7bfa7..2cef99a 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -2294,7 +2294,8 @@ enum {
    > };
    >
    > static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
    > - unsigned int nr_pages, bool oom_check)
    > + unsigned int nr_pages, unsigned int min_pages,
    > + bool oom_check)
    > {
    > unsigned long csize = nr_pages * PAGE_SIZE;
    > struct mem_cgroup *mem_over_limit;
    > @@ -2317,18 +2318,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
    > } else
    > mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
    > /*
    > - * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
    > - * of regular pages (CHARGE_BATCH), or a single regular page (1).
    > - *
    > * Never reclaim on behalf of optional batching, retry with a
    > * single page instead.
    > */
    > - if (nr_pages == CHARGE_BATCH)
    > + if (nr_pages > min_pages)
    > return CHARGE_RETRY;
    >
    > if (!(gfp_mask & __GFP_WAIT))
    > return CHARGE_WOULDBLOCK;
    >
    > + if (gfp_mask & __GFP_NORETRY)
    > + return CHARGE_NOMEM;
    > +
    > ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
    > if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
    > return CHARGE_RETRY;
    > @@ -2341,7 +2342,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
    > * unlikely to succeed so close to the limit, and we fall back
    > * to regular pages anyway in case of failure.
    > */
    > - if (nr_pages == 1 && ret)
    > + if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret)
    > return CHARGE_RETRY;
    >
    > /*
    > @@ -2476,7 +2477,8 @@ again:
    > nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
    > }
    >
    > - ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
    > + ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
    > + oom_check);
    > switch (ret) {
    > case CHARGE_OK:
    > break;
    > --
    > 1.7.11.2
    >
    > --
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    --
    Michal Hocko
    SUSE Labs


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