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    Subject[PATCH 02/11] memcg: Reclaim when more than one page needed.
    Date
    From: Suleiman Souhlal <ssouhlal@FreeBSD.org>

    mem_cgroup_do_charge() was written before slab 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 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), stay safe with a cond_resched(),
    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>
    ---
    mm/memcontrol.c | 23 ++++++++++++++++-------
    1 file changed, 16 insertions(+), 7 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 9304db2..8e601e8 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -2158,8 +2158,16 @@ enum {
    CHARGE_OOM_DIE, /* the current is killed because of OOM */
    };

    +/*
    + * We need a number that is small enough to be likely to have been
    + * reclaimed even under pressure, but not too big to trigger unnecessary
    + * retries
    + */
    +#define NR_PAGES_TO_RETRY 2
    +
    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;
    @@ -2182,18 +2190,18 @@ 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;
    @@ -2206,7 +2214,7 @@ 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 <= NR_PAGES_TO_RETRY && ret)
    return CHARGE_RETRY;

    /*
    @@ -2341,7 +2349,8 @@ 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;
    --
    1.7.10.2


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