On Tue, Oct 11, 2016 at 08:50:48AM +0200, Michal Hocko wrote: > On Tue 11-10-16 14:01:41, Minchan Kim wrote: > > Hi Michal, > > > > On Mon, Oct 10, 2016 at 09:41:40AM +0200, Michal Hocko wrote: > > > On Fri 07-10-16 23:43:45, Minchan Kim wrote: > > > > On Fri, Oct 07, 2016 at 11:09:17AM +0200, Michal Hocko wrote: > [...] > > > > > @@ -2102,10 +2109,12 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac) > > > > > set_pageblock_migratetype(page, ac->migratetype); > > > > > move_freepages_block(zone, page, ac->migratetype); > > > > > spin_unlock_irqrestore(&zone->lock, flags); > > > > > - return; > > > > > + return true; > > > > > > > > Such cut-off makes reserved pageblock remained before the OOM. > > > > We call it as premature OOM kill. > > > > > > Not sure I understand. The above should get rid of all atomic reserves > > > before we go OOM. We can do it all at once but that sounds too > > > > The problem is there is race between page freeing path and unreserve > > logic so that some pages could be in highatomic free list even though > > zone->nr_reserved_highatomic is already zero. > > Does it make any sense to handle such an unlikely case? I agree if it's really hard to solve but why should we remain such hole in the algorithm if we can fix easily? > > > So, at least, it would be better to have a draining step at some point > > where was (no_progress_loops == MAX_RECLAIM RETRIES) in my patch. > > > > Also, your patch makes retry loop greater than MAX_RECLAIM_RETRIES > > if unreserve_highatomic_pageblock returns true. Theoretically, > > it would make live lock. You might argue it's *really really* rare > > but I don't want to add such subtle thing. > > Maybe, we could drain when no_progress_loops == MAX_RECLAIM_RETRIES. > > What would be the scenario when we would really livelock here? How can > we have unreserve_highatomic_pageblock returning true for ever? Other context freeing highorder page/reallocating repeatedly while a process stucked direct reclaim is looping with should_reclaim_retry. > > > > aggressive to me. If we just do one at the time we have a chance to > > > keep some reserves if the OOM situation is really ephemeral. > > > > > > Does this patch work in your usecase? > > > > I didn't test but I guess it works but it has problems I mentioned > > above. > > Please do not make this too over complicated and be practical. I do not > really want to dismiss your usecase but I am really not convinced that > such a "perfectly fit into all memory" situations are sustainable and > justify to make the whole code more complex. I agree that we can at > least try to do something to release those reserves but let's do it > as simple as possible. If you think it's too complicated, how about this? diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fd91b8955b26..e3ce442e9976 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2098,7 +2098,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone, * intense memory pressure but failed atomic allocations should be easier * to recover from than an OOM. */ -static void unreserve_highatomic_pageblock(const struct alloc_context *ac) +static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, + bool drain) { struct zonelist *zonelist = ac->zonelist; unsigned long flags; @@ -2106,11 +2107,12 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac) struct zone *zone; struct page *page; int order; + bool ret = false; for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->high_zoneidx, ac->nodemask) { /* Preserve at least one pageblock */ - if (zone->nr_reserved_highatomic <= pageblock_nr_pages) + if (!drain && zone->nr_reserved_highatomic <= pageblock_nr_pages) continue; spin_lock_irqsave(&zone->lock, flags); @@ -2154,12 +2156,24 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac) * may increase. */ set_pageblock_migratetype(page, ac->migratetype); - move_freepages_block(zone, page, ac->migratetype); - spin_unlock_irqrestore(&zone->lock, flags); - return; + ret = move_freepages_block(zone, page, + ac->migratetype); + /* + * By race with page freeing functions, !highatomic + * pageblocks can have free pages in highatomic free + * list so if drain is true, try to unreserve every + * free pages in highatomic free list without bailing + * out. + */ + if (!drain) { + spin_unlock_irqrestore(&zone->lock, flags); + return ret; + } } spin_unlock_irqrestore(&zone->lock, flags); } + + return ret; } /* Remove an element from the buddy allocator from the fallback list */ @@ -3358,7 +3372,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order, * Shrink them them and try again */ if (!page && !drained) { - unreserve_highatomic_pageblock(ac); + unreserve_highatomic_pageblock(ac, false); drain_all_pages(NULL); drained = true; goto retry; @@ -3475,8 +3489,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order, * Make sure we converge to OOM if we cannot make any progress * several times in the row. */ - if (*no_progress_loops > MAX_RECLAIM_RETRIES) + if (*no_progress_loops > MAX_RECLAIM_RETRIES) { + if (unreserve_highatomic_pageblock(ac, true)) + return true; return false; + } /* * Keep reclaiming pages while there is a chance this will lead > > -- > Michal Hocko > SUSE Labs > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>