Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966140AbbDXTOI (ORCPT ); Fri, 24 Apr 2015 15:14:08 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:47041 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932461AbbDXTOE (ORCPT ); Fri, 24 Apr 2015 15:14:04 -0400 Date: Fri, 24 Apr 2015 15:13:53 -0400 From: Johannes Weiner To: Michal Hocko Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton , Tetsuo Handa , Huang Ying , Andrea Arcangeli , Dave Chinner , "Theodore Ts'o" Subject: Re: [patch 09/12] mm: page_alloc: private memory reserves for OOM-killing allocations Message-ID: <20150424191353.GA5293@cmpxchg.org> References: <1427264236-17249-1-git-send-email-hannes@cmpxchg.org> <1427264236-17249-10-git-send-email-hannes@cmpxchg.org> <20150414164939.GJ17160@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150414164939.GJ17160@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2591 Lines: 54 On Tue, Apr 14, 2015 at 06:49:40PM +0200, Michal Hocko wrote: > On Wed 25-03-15 02:17:13, Johannes Weiner wrote: > > @@ -5747,17 +5765,18 @@ static void __setup_per_zone_wmarks(void) > > > > min_pages = zone->managed_pages / 1024; > > min_pages = clamp(min_pages, SWAP_CLUSTER_MAX, 128UL); > > - zone->watermark[WMARK_MIN] = min_pages; > > + zone->watermark[WMARK_OOM] = min_pages; > > } else { > > /* > > * If it's a lowmem zone, reserve a number of pages > > * proportionate to the zone's size. > > */ > > - zone->watermark[WMARK_MIN] = tmp; > > + zone->watermark[WMARK_OOM] = tmp; > > } > > > > - zone->watermark[WMARK_LOW] = min_wmark_pages(zone) + (tmp >> 2); > > - zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp >> 1); > > + zone->watermark[WMARK_MIN] = oom_wmark_pages(zone) + (tmp >> 3); > > + zone->watermark[WMARK_LOW] = oom_wmark_pages(zone) + (tmp >> 2); > > + zone->watermark[WMARK_HIGH] = oom_wmark_pages(zone) + (tmp >> 1); > > This will basically elevate the min watermark, right? And that might lead > to subtle performance differences even when OOM killer is not invoked > because the direct reclaim will start sooner. It will move the min watermark a bit closer to the kswapd watermarks, so I guess the risk of entering direct reclaim when kswapd won't wake up fast enough before concurrent allocator slowpaths deplete the zone from low to min is marginally increased. That seems like a farfetched worry, especially given that waking up a sleeping kswapd is not a high frequency event in the first place. > Shouldn't we rather give WMARK_OOM half of WMARK_MIN instead? I guess conceptually that would work as well, since an OOM killing task is technically reclaiming memory and this reserve is meant to help reclaiming tasks make forward progress. That being said, the separate OOM reserve was designed for when the allocation can actually fail: deplete our own little reserve before returning failure. But it looks like neither the low-order nor the GFP_NOFS deadlock fixes got any traction, and so right now all OOM killing allocations still have the potential to deadlock. Is there a reason we shouldn't just let them do an ALLOC_NO_WATERMARK allocation after the OOM victim exited (or timed out)? Otherwise, I'll just do that in the next iteration. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/