Messages in this thread | | | Date | Thu, 3 Dec 2015 10:17:19 +0000 | From | Mel Gorman <> | Subject | Re: [lkp] [mm, page_alloc] d0164adc89: -100.0% fsmark.app_overhead |
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On Thu, Dec 03, 2015 at 04:46:53PM +0800, Huang, Ying wrote: > Mel Gorman <mgorman@techsingularity.net> writes: > > > On Wed, Dec 02, 2015 at 03:15:29PM +0100, Michal Hocko wrote: > >> > > I didn't mention this allocation failure because I am not sure it is > >> > > really related. > >> > > > >> > > >> > I'm fairly sure it is. The failure is an allocation site that cannot > >> > sleep but did not specify __GFP_HIGH. > >> > >> yeah but this was the case even before your patch. As the caller used > >> GFP_ATOMIC then it got __GFP_ATOMIC after your patch so it still > >> managed to do ALLOC_HARDER. I would agree if this was an explicit > >> GFP_NOWAIT. Unless I am missing something your patch hasn't changed the > >> behavior for this particular allocation. > >> > > > > You're right. I think it's this hunk that is the problem. > > > > @@ -1186,7 +1186,7 @@ static struct request *blk_mq_map_request(struct > > request_queue *q, > > ctx = blk_mq_get_ctx(q); > > hctx = q->mq_ops->map_queue(q, ctx->cpu); > > blk_mq_set_alloc_data(&alloc_data, q, > > - __GFP_WAIT|GFP_ATOMIC, false, ctx, hctx); > > + __GFP_WAIT|__GFP_HIGH, false, ctx, hctx); > > rq = __blk_mq_alloc_request(&alloc_data, rw); > > ctx = alloc_data.ctx; > > hctx = alloc_data.hctx; > > > > This specific path at this patch is not waking kswapd any more when it > > should. A series of allocations there could hit the watermarks and never wake > > kswapd and then be followed by an atomic allocation failure that woke kswapd. > > > > This bug gets fixed later by the commit 71baba4b92dc ("mm, page_alloc: > > rename __GFP_WAIT to __GFP_RECLAIM") so it's not a bug in the current > > kernel. However, it happens to break bisection and would be caught if each > > individual commit was tested. > > > > Your __GFP_HIGH patch is still fine although not the direct fix for this > > specific problem. Commit 71baba4b92dc is. > > > > Ying, does the page allocation failure messages happen when the whole > > series is applied? i.e. is 4.4-rc3 ok? > > There are allocation errors for 4.4-rc3 too. dmesg is attached. >
What is the result of the __GFP_HIGH patch to give it access to reserves?
-- Mel Gorman SUSE Labs
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