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Date: Tue, 15 Dec 2020 17:45:40 +0100 From: Johannes Weiner <hannes@...xchg.org> To: Kirill Tkhai <tkhai@...ru> Cc: Yang Shi <shy828301@...il.com>, "guro@...com" <guro@...com>, "ktkhai@...tuozzo.com" <ktkhai@...tuozzo.com>, "shakeelb@...gle.com" <shakeelb@...gle.com>, "david@...morbit.com" <david@...morbit.com>, "mhocko@...e.com" <mhocko@...e.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [v2 PATCH 3/9] mm: vmscan: guarantee shrinker_slab_memcg() sees valid shrinker_maps for online memcg On Tue, Dec 15, 2020 at 03:58:06PM +0300, Kirill Tkhai wrote: > 15.12.2020, 15:40, "Johannes Weiner" <hannes@...xchg.org>: > > On Mon, Dec 14, 2020 at 02:37:16PM -0800, Yang Shi wrote: > >> The shrink_slab_memcg() races with mem_cgroup_css_online(). A visibility of CSS_ONLINE flag > >> in shrink_slab_memcg()->mem_cgroup_online() does not guarantee that we will see > >> memcg->nodeinfo[nid]->shrinker_maps != NULL. This may occur because of processor reordering > >> on !x86. > >> > >> This seems like the below case: > >> > >> CPU A CPU B > >> store shrinker_map load CSS_ONLINE > >> store CSS_ONLINE load shrinker_map > >> > >> So the memory ordering could be guaranteed by smp_wmb()/smp_rmb() pair. > >> > >> The memory barriers pair will guarantee the ordering between shrinker_deferred and CSS_ONLINE > >> for the following patches as well. > >> > >> Signed-off-by: Yang Shi <shy828301@...il.com> > > > > As per previous feedback, please move the misplaced shrinker > > allocation callback from .css_online to .css_alloc. This will get you > > the necessary ordering guarantees from the cgroup core code. > > > Can you read my emails from ktkhai@...tuozzo.com? I've already answered > on this question here: https://lkml.org/lkml/2020/12/10/726 > > Check your spam folder, and add my address to allow-list if so. It was indeed in my spam folder. Disregard what I wrote above.
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