From: Vlastimil Babka <vbabka@suse.cz> To: Michal Hocko <mhocko@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, David Rientjes <rientjes@google.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 2/2] mm: do not loop over ALLOC_NO_WATERMARKS without triggering reclaim Date: Wed, 18 Nov 2015 16:19:14 +0100 [thread overview] Message-ID: <564C96F2.10102@suse.cz> (raw) In-Reply-To: <20151118151119.GG19145@dhcp22.suse.cz> On 11/18/2015 04:11 PM, Michal Hocko wrote: > On Wed 18-11-15 15:57:45, Vlastimil Babka wrote: > [...] >> > --- a/mm/page_alloc.c >> > +++ b/mm/page_alloc.c >> > @@ -3046,32 +3046,36 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, >> > * allocations are system rather than user orientated >> > */ >> > ac->zonelist = node_zonelist(numa_node_id(), gfp_mask); >> > - do { >> > - page = get_page_from_freelist(gfp_mask, order, >> > - ALLOC_NO_WATERMARKS, ac); >> > - if (page) >> > - goto got_pg; >> > - >> > - if (gfp_mask & __GFP_NOFAIL) >> > - wait_iff_congested(ac->preferred_zone, >> > - BLK_RW_ASYNC, HZ/50); >> >> I've been thinking if the lack of unconditional wait_iff_congested() can affect >> something negatively. I guess not? > > Considering that the wait_iff_congested is removed only for PF_MEMALLOC > with __GFP_NOFAIL which should be non-existent in the kernel then I Hm that one won't reach it indeed, but also not loop, so that wasn't my concern. I was referring to: /* Keep reclaiming pages as long as there is reasonable progress */ pages_reclaimed += did_some_progress; if ((did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER) || ((gfp_mask & __GFP_REPEAT) && pages_reclaimed < (1 << order))) { /* Wait for some write requests to complete then retry */ wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50); goto retry; } Here we might skip the wait_iff_congested and go straight for oom. But it's true that ordinary allocations that fail to make progress will also not wait, so I guess it's fine. Acked-by: Vlastimil Babka <vbabka@suse.cz> > think the risk is really low. Even if there was a caller _and_ there > was a congestion then the behavior wouldn't be much more worse than > what we have currently. The system is out of memory hoplessly if > ALLOC_NO_WATERMARKS allocation fails. >
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz> To: Michal Hocko <mhocko@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, David Rientjes <rientjes@google.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 2/2] mm: do not loop over ALLOC_NO_WATERMARKS without triggering reclaim Date: Wed, 18 Nov 2015 16:19:14 +0100 [thread overview] Message-ID: <564C96F2.10102@suse.cz> (raw) In-Reply-To: <20151118151119.GG19145@dhcp22.suse.cz> On 11/18/2015 04:11 PM, Michal Hocko wrote: > On Wed 18-11-15 15:57:45, Vlastimil Babka wrote: > [...] >> > --- a/mm/page_alloc.c >> > +++ b/mm/page_alloc.c >> > @@ -3046,32 +3046,36 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, >> > * allocations are system rather than user orientated >> > */ >> > ac->zonelist = node_zonelist(numa_node_id(), gfp_mask); >> > - do { >> > - page = get_page_from_freelist(gfp_mask, order, >> > - ALLOC_NO_WATERMARKS, ac); >> > - if (page) >> > - goto got_pg; >> > - >> > - if (gfp_mask & __GFP_NOFAIL) >> > - wait_iff_congested(ac->preferred_zone, >> > - BLK_RW_ASYNC, HZ/50); >> >> I've been thinking if the lack of unconditional wait_iff_congested() can affect >> something negatively. I guess not? > > Considering that the wait_iff_congested is removed only for PF_MEMALLOC > with __GFP_NOFAIL which should be non-existent in the kernel then I Hm that one won't reach it indeed, but also not loop, so that wasn't my concern. I was referring to: /* Keep reclaiming pages as long as there is reasonable progress */ pages_reclaimed += did_some_progress; if ((did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER) || ((gfp_mask & __GFP_REPEAT) && pages_reclaimed < (1 << order))) { /* Wait for some write requests to complete then retry */ wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50); goto retry; } Here we might skip the wait_iff_congested and go straight for oom. But it's true that ordinary allocations that fail to make progress will also not wait, so I guess it's fine. Acked-by: Vlastimil Babka <vbabka@suse.cz> > think the risk is really low. Even if there was a caller _and_ there > was a congestion then the behavior wouldn't be much more worse than > what we have currently. The system is out of memory hoplessly if > ALLOC_NO_WATERMARKS allocation fails. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2015-11-18 15:19 UTC|newest] Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-11-16 13:22 [PATCH 0/2] get rid of __alloc_pages_high_priority mhocko 2015-11-16 13:22 ` mhocko 2015-11-16 13:22 ` [PATCH 1/2] mm: " mhocko 2015-11-16 13:22 ` mhocko 2015-11-16 18:43 ` Mel Gorman 2015-11-16 18:43 ` Mel Gorman 2015-11-16 21:14 ` David Rientjes 2015-11-16 21:14 ` David Rientjes 2015-11-18 14:48 ` Vlastimil Babka 2015-11-18 14:48 ` Vlastimil Babka 2015-11-16 13:22 ` [PATCH 2/2] mm: do not loop over ALLOC_NO_WATERMARKS without triggering reclaim mhocko 2015-11-16 13:22 ` mhocko 2015-11-16 21:18 ` David Rientjes 2015-11-16 21:18 ` David Rientjes 2015-11-17 10:58 ` Tetsuo Handa 2015-11-17 10:58 ` Tetsuo Handa 2015-11-18 9:11 ` Michal Hocko 2015-11-18 9:11 ` Michal Hocko 2015-11-18 9:22 ` Michal Hocko 2015-11-18 9:22 ` Michal Hocko 2015-11-18 14:57 ` Vlastimil Babka 2015-11-18 14:57 ` Vlastimil Babka 2015-11-18 15:11 ` Michal Hocko 2015-11-18 15:11 ` Michal Hocko 2015-11-18 15:19 ` Vlastimil Babka [this message] 2015-11-18 15:19 ` Vlastimil Babka 2015-11-23 9:33 ` Michal Hocko 2015-11-23 9:33 ` Michal Hocko
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