linux-kernel - Re: [PATCH v2 1/7] fs/proc/page: remove unneeded PageTail && PageSlab check

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Message-ID: <ZU5yROwNmTZpyxb8@casper.infradead.org>
Date:   Fri, 10 Nov 2023 18:11:16 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>,
        Gregory Price <gregory.price@...verge.com>
Subject: Re: [PATCH v2 1/7] fs/proc/page: remove unneeded PageTail &&
 PageSlab check

On Fri, Nov 10, 2023 at 11:33:18AM +0800, Kefeng Wang wrote:
> After commit dcb351cd095a ("page-flags: define behavior SL*B-related
> flags on compound pages"), the slab could not be a tail, remove unneeded
> PageTail && PageSlab check.

No, that's completely wrong.

 * PF_NO_TAIL:
 *     modifications of the page flag must be done on small or head pages,
 *     checks can be done on tail pages too.

That's backed up by the code:

#define PF_NO_TAIL(page, enforce) ({                                    \
                VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);     \
                PF_POISONED_CHECK(compound_head(page)); })

(enforce is set to 0 for the 'test')

> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>

NAK