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Date:   Mon, 8 Nov 2021 09:42:45 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
Subject: Re:
 vfs-keep-inodes-with-page-cache-off-the-inode-shrinker-lru.patch
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On Mon, 8 Nov 2021 10:57:23 -0500 Johannes Weiner <hannes@cmpxchg.org> wrote:

> Hi Andrew,
> 
> I promised to give this patch some more testing exposure while it sits
> in -mm. We've been steadily rolling this version of the change to our
> fleet over the last months and it's currently on 20% of FB servers. We
> have not noticed crashes or performance regressions because of it.
> (The other 80% is running a previous version of the patch.)
> 
> The comment in 'series' says "extra cycle" but that was 5.15 :-) Do
> you think we can get it merged into 5.16?
> 
> Just to reiterate, without the patch, there is very broad production
> breakage for FB beyond reduced cache effectiveness. Yes, we lose cache
> pages prematurely. But a bigger problem is that we lose nonresident
> info we store in the inodes. This defeats thrash detection, which in
> turn defeats psi and central reclaim deciscion making. The downstream
> effects of this are quite severe and widespread:
> 
> - memory prioity inversion between containers
> - failure to offload cold memory to swap with proactive reclaim
> - breakdown of container health monitoring and userspace OOM killing
> 
> I'm not exaggerating when I say we can't reliably operate our fleet
> without this patch. We've had to carry variants of it for two years
> now. It'd be great to get this fixed upstream.

Cool, thanks for the update.  I'll sent it Linuswards this week.