linux-kernel - Re: [PATCH RFC] mm: mglru: provide a separate list for lazyfree anon folios

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Message-ID: <92f97c8e-f23d-4c6e-9f49-230fb4e96c46@redhat.com>
Date: Tue, 17 Sep 2024 14:02:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org
Cc: mhocko@...e.com, fengbaopeng@...or.com, gaoxu2@...or.com,
 hailong.liu@...o.com, kaleshsingh@...gle.com, linux-kernel@...r.kernel.org,
 lokeshgidra@...gle.com, ngeoffray@...gle.com, shli@...com,
 surenb@...gle.com, yipengxiang@...or.com, yuzhao@...gle.com,
 minchan@...nel.org, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH RFC] mm: mglru: provide a separate list for lazyfree anon
 folios

On 14.09.24 08:37, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> This follows up on the discussion regarding Gaoxu's work[1]. It's
> unclear if there's still interest in implementing a separate LRU
> list for lazyfree folios, but I decided to explore it out of
> curiosity.
> 
> According to Lokesh, MADV_FREE'd anon folios are expected to be
> released earlier than file folios. One option, as implemented
> by Gao Xu, is to place lazyfree anon folios at the tail of the
> file's `min_seq` generation. However, this approach results in
> lazyfree folios being released in a LIFO manner, which conflicts
> with LRU behavior, as noted by Michal.
> 
> To address this, this patch proposes maintaining a separate list
> for lazyfree anon folios while keeping them classified under the
> "file" LRU type to minimize code changes. These lazyfree anon
> folios will still be counted as file folios and share the same
> generation with regular files. In the eviction path, the lazyfree
> list will be prioritized for scanning before the actual file
> LRU list.
> 

What's the downside of another LRU list? Do we have any experience on that?

-- 
Cheers,

David / dhildenb