From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [PATCH 2/3] mm: vmscan: detect file thrashing at the reclaim root Date: Wed, 12 Feb 2020 13:18:34 -0500 Message-ID: <20200212181834.GD180867@cmpxchg.org> References: <20191107205334.158354-1-hannes@cmpxchg.org> <20191107205334.158354-3-hannes@cmpxchg.org> <20200212102817.GA18107@js1304-desktop> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=OWGcBq+RmtovTTracPqR5yMhReLnPEQNRqBqlsGYoqQ=; b=y2gv+7sTsHniWkrRXHbMycwPBOZkSVEUBxS0FbQa9VB6OPJaYJ1Ny9M6xr/G2DVX+A 2y3zu+4t8K+YEOEZiGZ16SmwaFBkHE7wfdPJ73oAGMEcRLyA7SdYtUq2rlqAIOJ7AlQ+ UybJYIDz3qsZGxZfUM1AtJQB0pELtShzFC9k3aLs7g4W9U5IbFUlcjQfKEHGvhzfclm+ JveHX0RcnHpMZXSqGvlbSX7VBuxQcKiVaV6YvUnzx7SOAGPdgFUsRDnB4h3byEIPdOR4 Deg6SO3d+i3NoTjYxf140EY5fK1CDhyhjBV3mFZrOFF2taWoChENIoAjBrb9azCLuXXz mScA== Content-Disposition: inline In-Reply-To: <20200212102817.GA18107@js1304-desktop> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Joonsoo Kim Cc: Andrew Morton , Andrey Ryabinin , Suren Baghdasaryan , Shakeel Butt , Rik van Riel , Michal Hocko , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org On Wed, Feb 12, 2020 at 07:28:19PM +0900, Joonsoo Kim wrote: > Hello, Johannes. > > When I tested my patchset on v5.5, I found that my patchset doesn't > work as intended. I tracked down the issue and this patch would be the > reason of unintended work. I don't fully understand the patchset so I > could be wrong. Please let me ask some questions. > > On Thu, Nov 07, 2019 at 12:53:33PM -0800, Johannes Weiner wrote: > ...snip... > > -static void snapshot_refaults(struct mem_cgroup *root_memcg, pg_data_t *pgdat) > > +static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat) > > { > > - struct mem_cgroup *memcg; > > - > > - memcg = mem_cgroup_iter(root_memcg, NULL, NULL); > > - do { > > - unsigned long refaults; > > - struct lruvec *lruvec; > > + struct lruvec *target_lruvec; > > + unsigned long refaults; > > > > - lruvec = mem_cgroup_lruvec(memcg, pgdat); > > - refaults = lruvec_page_state_local(lruvec, WORKINGSET_ACTIVATE); > > - lruvec->refaults = refaults; > > - } while ((memcg = mem_cgroup_iter(root_memcg, memcg, NULL))); > > + target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat); > > + refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE); > > + target_lruvec->refaults = refaults; > > Is it correct to just snapshot the refault for the target memcg? I > think that we need to snapshot the refault for all the child memcgs > since we have traversed all the child memcgs with the refault count > that is aggregration of all the child memcgs. If next reclaim happens > from the child memcg, workingset transition that is already considered > could be considered again. Good catch, you're right! We have to update all cgroups in the tree, like we used to. However, we need to use lruvec_page_state() instead of _local, because we do recursive comparisons in shrink_node()! So it's not a clean revert of that hunk. Does this patch here fix the problem you are seeing? diff --git a/mm/vmscan.c b/mm/vmscan.c index c82e9831003f..e7431518db13 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2993,12 +2993,17 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc) static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat) { - struct lruvec *target_lruvec; - unsigned long refaults; + struct mem_cgroup *memcg; - target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat); - refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE); - target_lruvec->refaults = refaults; + memcg = mem_cgroup_iter(target_memcg, NULL, NULL); + do { + unsigned long refaults; + struct lruvec *lruvec; + + lruvec = mem_cgroup_lruvec(memcg, pgdat); + refaults = lruvec_page_state(lruvec, WORKINGSET_ACTIVATE); + lruvec->refaults = refaults; + } while ((memcg = mem_cgroup_iter(target_memcg, memcg, NULL))); } /* > > @@ -277,12 +305,12 @@ void workingset_refault(struct page *page, void *shadow) > > * would be better if the root_mem_cgroup existed in all > > * configurations instead. > > */ > > - memcg = mem_cgroup_from_id(memcgid); > > - if (!mem_cgroup_disabled() && !memcg) > > + eviction_memcg = mem_cgroup_from_id(memcgid); > > + if (!mem_cgroup_disabled() && !eviction_memcg) > > goto out; > > - lruvec = mem_cgroup_lruvec(memcg, pgdat); > > - refault = atomic_long_read(&lruvec->inactive_age); > > - active_file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES); > > + eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat); > > + refault = atomic_long_read(&eviction_lruvec->inactive_age); > > + active_file = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE); > > Do we need to use the aggregation LRU count of all the child memcgs? > AFAIU, refault here is the aggregation counter of all the related > memcgs. Without using the aggregation count for LRU, active_file could > be so small than the refault distance and refault cannot happen > correctly. lruvec_page_state() *is* aggregated for all child memcgs (as opposed to lruvec_page_state_local()), so that comparison looks correct to me.