From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id E3A006B0003 for ; Mon, 5 Nov 2018 09:23:13 -0500 (EST) Received: by mail-qk1-f199.google.com with SMTP id n68so21208377qkn.8 for ; Mon, 05 Nov 2018 06:23:13 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 42si503565qvd.29.2018.11.05.06.23.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Nov 2018 06:23:12 -0800 (PST) Date: Mon, 5 Nov 2018 22:23:08 +0800 From: Baoquan He Subject: Re: [PATCH] mm, memory_hotplug: teach has_unmovable_pages about of LRU migrateable pages Message-ID: <20181105142308.GJ27491@MiWiFi-R3L-srv> References: <20181101091055.GA15166@MiWiFi-R3L-srv> <20181102155528.20358-1-mhocko@kernel.org> <20181105002009.GF27491@MiWiFi-R3L-srv> <20181105091407.GB4361@dhcp22.suse.cz> <20181105092851.GD4361@dhcp22.suse.cz> <20181105102520.GB22011@MiWiFi-R3L-srv> <20181105123837.GH4361@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181105123837.GH4361@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , linux-mm@kvack.org, LKML , Stable tree On 11/05/18 at 01:38pm, Michal Hocko wrote: > On Mon 05-11-18 18:25:20, Baoquan He wrote: > > Hi Michal, > > > > On 11/05/18 at 10:28am, Michal Hocko wrote: > > > > > > Or something like this. Ugly as hell, no question about that. I also > > > have to think about this some more to convince myself this will not > > > result in an endless loop under some situations. > > > > It failed. Paste the log and patch diff here, please help check if I made > > any mistake on manual code change. The log is at bottom. > > The retry patch is obviously still racy, it just makes the race window > slightly smaller and I hoped it would catch most of those races but this > is obviously not the case. > > I was thinking about your MIGRATE_MOVABLE check some more and I still do > not like it much, we just change migrate type at many places and I have > hard time to actually see this is always safe wrt. to what we need here. > > We should be able to restore the zone type check though. The > primary problem fixed by 15c30bc09085 ("mm, memory_hotplug: make > has_unmovable_pages more robust") was that early allocations made it to > the zone_movable range. If we add the check _after_ the PageReserved() > check then we should be able to rule all bootmem allocation out. > > So what about the following (on top of the previous patch which makes > sense on its own I believe). Yes, I think this looks very reasonable and should be robust. Have tested it, hot removing 4 hotpluggable nodes continusously succeeds, and then hot adding them back, still works well. So please feel free to add my Tested-by or Acked-by. Tested-by: Baoquan He or Acked-by: Baoquan He Thanks, Michal. > > > From d7ffd1342529c892f1de8999c3a5609211599c9d Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Mon, 5 Nov 2018 13:28:51 +0100 > Subject: [PATCH] mm, memory_hotplug: check zone_movable in has_unmovable_pages > > Page state checks are racy. Under a heavy memory workload (e.g. stress > -m 200 -t 2h) it is quite easy to hit a race window when the page is > allocated but its state is not fully populated yet. A debugging patch to > dump the struct page state shows > : [ 476.575516] has_unmovable_pages: pfn:0x10dfec00, found:0x1, count:0x0 > : [ 476.582103] page:ffffea0437fb0000 count:1 mapcount:1 mapping:ffff880e05239841 index:0x7f26e5000 compound_mapcount: 1 > : [ 476.592645] flags: 0x5fffffc0090034(uptodate|lru|active|head|swapbacked) > > Note that the state has been checked for both PageLRU and PageSwapBacked > already. Closing this race completely would require some sort of retry > logic. This can be tricky and error prone (think of potential endless > or long taking loops). > > Workaround this problem for movable zones at least. Such a zone should > only contain movable pages. 15c30bc09085 ("mm, memory_hotplug: make > has_unmovable_pages more robust") has told us that this is not strictly > true though. Bootmem pages should be marked reserved though so we can > move the original check after the PageReserved check. Pages from other > zones are still prone to races but we even do not pretend that memory > hotremove works for those so pre-mature failure doesn't hurt that much. > > Reported-by: Baoquan He > Signed-off-by: Michal Hocko > --- > mm/page_alloc.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 48ceda313332..5b64c5bc6ea0 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7788,6 +7788,14 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, > if (PageReserved(page)) > goto unmovable; > > + /* > + * If the zone is movable and we have ruled out all reserved > + * pages then it should be reasonably safe to assume the rest > + * is movable. > + */ > + if (zone_idx(zone) == ZONE_MOVABLE) > + continue; > + > /* > * Hugepages are not in LRU lists, but they're movable. > * We need not scan over tail pages bacause we don't > -- > 2.19.1 > > -- > Michal Hocko > SUSE Labs