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    SubjectRe: [PATCH v6 15/17] mm: Generalize shrink_slab() calls in shrink_node()
    On Fri, May 18, 2018 at 11:44:11AM +0300, Kirill Tkhai wrote:
    > From: Vladimir Davydov <vdavydov.dev@gmail.com>
    >
    > The patch makes shrink_slab() be called for root_mem_cgroup
    > in the same way as it's called for the rest of cgroups.
    > This simplifies the logic and improves the readability.
    >
    > Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
    > ktkhai: Description written.
    > Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
    > ---
    > mm/vmscan.c | 13 +++----------
    > 1 file changed, 3 insertions(+), 10 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 2fbf3b476601..f1d23e2df988 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c

    You forgot to patch the comment to shrink_slab(). Please take a closer
    look at the diff I sent you:

    @@ -486,10 +486,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
    * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
    * unaware shrinkers will receive a node id of 0 instead.
    *
    - * @memcg specifies the memory cgroup to target. If it is not NULL,
    - * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
    - * objects from the memory cgroup specified. Otherwise, only unaware
    - * shrinkers are called.
    + * @memcg specifies the memory cgroup to target. Unaware shrinkers
    + * are called only if it is the root cgroup.
    *
    * @priority is sc->priority, we take the number of objects and >> by priority
    * in order to get the scan target.

    > @@ -661,9 +661,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
    > .memcg = memcg,
    > };

    If you made !MEMCG version of mem_cgroup_is_root return true, as I
    suggested in reply to patch 13, you could also simplify the memcg
    related check in the beginning of shrink_slab() as in case of
    CONFIG_MEMCG 'memcg' is now guaranteed to be != NULL in this function
    while in case if !CONFIG_MEMCG mem_cgroup_is_root() would always
    return true:

    @@ -501,7 +501,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
    struct shrinker *shrinker;
    unsigned long freed = 0;

    - if (memcg && !mem_cgroup_is_root(memcg))
    + if (!mem_cgroup_is_root(memcg))
    return shrink_slab_memcg(gfp_mask, nid, memcg, priority);

    if (!down_read_trylock(&shrinker_rwsem))

    >
    > - if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
    > - continue;
    > -
    > if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
    > sc.nid = 0;
    >
    > @@ -693,6 +690,7 @@ void drop_slab_node(int nid)
    > struct mem_cgroup *memcg = NULL;
    >
    > freed = 0;
    > + memcg = mem_cgroup_iter(NULL, NULL, NULL);
    > do {
    > freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
    > } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
    > @@ -2712,9 +2710,8 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
    > shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
    > node_lru_pages += lru_pages;
    >
    > - if (memcg)
    > - shrink_slab(sc->gfp_mask, pgdat->node_id,
    > - memcg, sc->priority);
    > + shrink_slab(sc->gfp_mask, pgdat->node_id,
    > + memcg, sc->priority);
    >
    > /* Record the group's reclaim efficiency */
    > vmpressure(sc->gfp_mask, memcg, false,
    > @@ -2738,10 +2735,6 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
    > }
    > } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
    >
    > - if (global_reclaim(sc))
    > - shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
    > - sc->priority);
    > -
    > if (reclaim_state) {
    > sc->nr_reclaimed += reclaim_state->reclaimed_slab;
    > reclaim_state->reclaimed_slab = 0;
    >

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