linux-kernel - Re: [PATCH v1 0/5] percpu: partial chunk depopulation

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Message-ID: <9da8492f-2ffb-2d4f-c937-93df28f0215a@suse.cz>
Date:   Wed, 7 Apr 2021 13:09:47 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Roman Gushchin <guro@...com>, Dennis Zhou <dennis@...nel.org>
Cc:     Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 0/5] percpu: partial chunk depopulation

On 4/1/21 11:42 PM, Roman Gushchin wrote:
> In our production experience the percpu memory allocator is sometimes struggling
> with returning the memory to the system. A typical example is a creation of
> several thousands memory cgroups (each has several chunks of the percpu data
> used for vmstats, vmevents, ref counters etc). Deletion and complete releasing
> of these cgroups doesn't always lead to a shrinkage of the percpu memory.
> 
> The underlying problem is the fragmentation: to release an underlying chunk
> all percpu allocations should be released first. The percpu allocator tends
> to top up chunks to improve the utilization. It means new small-ish allocations
> (e.g. percpu ref counters) are placed onto almost filled old-ish chunks,
> effectively pinning them in memory.
> 
> This patchset pretends to solve this problem by implementing a partial

Really "pretends"? :) Or did you mean "attempts"?