Re: needed lru_add_drain_all() change

On Tue, 2012-06-26 at 23:46 -0700, Andrew Morton wrote:

btw, the first step should be to audit all lru_add_drain_all() sites
and work out exactly why they are calling lru_add_drain_all() - what
are they trying to achive?

# git grep lru_add_drain_all
fs/block_dev.c: lru_add_drain_all();    /* make sure all lru add caches are flushed */
include/linux/swap.h:extern int lru_add_drain_all(void);
mm/compaction.c:        lru_add_drain_all();
mm/compaction.c:                lru_add_drain_all();
mm/ksm.c:               lru_add_drain_all();
mm/memcontrol.c:                lru_add_drain_all();
mm/memcontrol.c:        lru_add_drain_all();
mm/memcontrol.c:        lru_add_drain_all();
mm/memory-failure.c:            lru_add_drain_all();
mm/memory_hotplug.c:            lru_add_drain_all();
mm/memory_hotplug.c:    lru_add_drain_all();
mm/migrate.c:   lru_add_drain_all();
mm/migrate.c:    * here to avoid lru_add_drain_all().
mm/mlock.c:     lru_add_drain_all();    /* flush pagevec */
mm/mlock.c:             lru_add_drain_all();    /* flush pagevec */
mm/page_alloc.c:         * For avoiding noise data, lru_add_drain_all() should be called
mm/page_alloc.c:        lru_add_drain_all();
mm/swap.c:int lru_add_drain_all(void)


I haven't audited all sites, but most of them try to flush the per-cpu
lru pagevecs to make sure the pages are on the lru so they can take them
off again ;-)

Take compaction for instance, if a page in the middle of a range is on a
per-cpu pagevec it can't move it and the compaction might fail.


Hmm, another alternative is teaching isolate_lru_page() and friends to
take pages from the pagevecs directly, not sure what that would take.

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