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    SubjectRe: [patch 08/11] mm: vmscan: convert global reclaim to per-memcg LRU lists
    On Wed, Sep 21, 2011 at 03:10:45PM +0200, Michal Hocko wrote:
    > On Mon 12-09-11 12:57:25, Johannes Weiner wrote:
    > > The global per-zone LRU lists are about to go away on memcg-enabled
    > > kernels, global reclaim must be able to find its pages on the
    > > per-memcg LRU lists.
    > >
    > > Since the LRU pages of a zone are distributed over all existing memory
    > > cgroups, a scan target for a zone is complete when all memory cgroups
    > > are scanned for their proportional share of a zone's memory.
    > >
    > > The forced scanning of small scan targets from kswapd is limited to
    > > zones marked unreclaimable, otherwise kswapd can quickly overreclaim
    > > by force-scanning the LRU lists of multiple memory cgroups.
    > >
    > > Signed-off-by: Johannes Weiner <jweiner@redhat.com>
    >
    > Reviewed-by: Michal Hocko <mhocko@suse.cz>

    Thanks

    > Minor nit bellow

    > > @@ -2451,13 +2445,24 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    > > static void age_active_anon(struct zone *zone, struct scan_control *sc,
    > > int priority)
    > > {
    > > - struct mem_cgroup_zone mz = {
    > > - .mem_cgroup = NULL,
    > > - .zone = zone,
    > > - };
    > > + struct mem_cgroup *mem;
    > > +
    > > + if (!total_swap_pages)
    > > + return;
    > > +
    > > + mem = mem_cgroup_iter(NULL, NULL, NULL);
    >
    > Wouldn't be for_each_mem_cgroup more appropriate? Macro is not exported
    > but probably worth exporting? The same applies for
    > scan_zone_unevictable_pages from the previous patch.

    Unfortunately, in generic code, these loops need to be layed out like
    this for !CONFIG_MEMCG to do the right thing. mem_cgroup_iter() will
    return NULL and the loop has to execute exactly once.

    This is something that will go away once we implement Christoph's
    suggestion of always having a (skeleton) root_mem_cgroup around, even
    for !CONFIG_MEMCG.


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