(2012/12/19 23:01), Glauber Costa wrote: > When we are out of space in the caches, we will try to allocate a new > page. If we still fail, the page allocator will try to free pages > through direct reclaim. Which means that if an object allocation failed > we can be sure that no new pages could be given to us, even though > direct reclaim was likely invoked. > > However, direct reclaim will also try to shrink objects from registered > shrinkers. They won't necessarily free a full page, but if our cache > happens to be one with a shrinker, this may very well open up the space > we need. So we retry the allocation in this case. > > We can't know for sure if this happened. So the best we can do is try to > derive from our allocation flags how likely it is for direct reclaim to > have been called, and retry if we conclude that this is highly likely > (GFP_NOWAIT | GFP_FS | !GFP_NORETRY). > > The common case is for the allocation to succeed. So we carefuly insert > a likely branch for that case. > > Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx> > CC: Christoph Lameter <cl@xxxxxxxxx> > CC: David Rientjes <rientjes@xxxxxxxxxx> > CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > CC: Mel Gorman <mgorman@xxxxxxx> > --- > mm/slab.c | 2 ++ > mm/slab.h | 42 ++++++++++++++++++++++++++++++++++++++++++ > mm/slob.c | 27 +++++++++++++++++++++++---- > mm/slub.c | 26 ++++++++++++++++++++------ > 4 files changed, 87 insertions(+), 10 deletions(-) > > diff --git a/mm/slab.c b/mm/slab.c > index a98295f..7e82f99 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -3535,6 +3535,8 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, > cache_alloc_debugcheck_before(cachep, flags); > local_irq_save(save_flags); > objp = __do_slab_alloc_node(cachep, flags, nodeid); > + if (slab_should_retry(objp, flags)) > + objp = __do_slab_alloc_node(cachep, flags, nodeid); 3 questions. 1. why can't we do retry in memcg's code (or kmem/memcg code) rather than slab.c ? 2. It should be retries even if memory allocator returns NULL page ? 3. What's relationship with oom-killer ? The first __do_slab_alloc() will not invoke oom-killer and returns NULL ? Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
