linux-kernel - Re: [PATCH] mm: remove offset check on page->compound

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Message-ID: <20220224010358.ttc2mgdevfqddvea@master>
Date:   Thu, 24 Feb 2022 01:03:58 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Wei Yang <richard.weiyang@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        peterz@...radead.org, will@...nel.org, linyunsheng@...wei.com,
        aarcange@...hat.com, feng.tang@...el.com, ebiederm@...ssion.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: remove offset check on page->compound_head and
 folio->lru

On Mon, Jan 24, 2022 at 11:30:10AM +0100, Vlastimil Babka wrote:
[...]
>> Hi, Matthew
>> 
>> Are you back from vocation? If you could give more insight on this check, I
>> would be appreciated.
>
>I can offer my insight (which might be of course wrong). Ideally one day
>page.lru will be gone and only folio will be used for LRU pages. Then there
>won't be a  FOLIO_MATCH(lru, lru); and FOLIO_MATCH(compound_head, lru);
>won't appear to be redundant anymore. lru is list_head so two pointers and
>thus valid pointers are aligned in such a way they can't accidentaly set the
>bit 0.
>

Hmm... I see your change on struct slab. I guess I got your point.

Seems we would shrink struct page...

-- 
Wei Yang
Help you, Help me