linux-kernel - Re: [PATCH v2 2/7] fs/proc/page: use a folio in stable_page

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Date:   Sat, 11 Nov 2023 11:21:14 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
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 2/7] fs/proc/page: use a folio in stable_page_flags()



On 2023/11/11 2:15, Matthew Wilcox wrote:
> On Fri, Nov 10, 2023 at 11:33:19AM +0800, Kefeng Wang wrote:
>> Replace nine compound_head() calls with one page_folio().
> 
> But that's not all it does.  Honestly, when you write these kind of
> things, I wonder if you understand what you're doing.

Oh, yes, I total wrong for some change, the kpagelfags should report
per-page.

> 
> After this patch, if we report on a tail page, we set (some of) the
> flags according to how its head page is set.  Before, we would have not
> reported on it at all.

I should force on the following specific flags in this patch

1) PageKsm
    - KSM only normal anon page, also it is wrapper of folio_test_ksm()
2) struct page *head = compound_head(page); PageLRU(head) PageAnon(head)
    - they expect to check the head page flags
3) page_count(page) == 0 && is_free_buddy_page(page)
    - this is to identify free buddy page, also page_count is a wrapper
      of folio_ref_count
4) page_is_idle
    - a wrapper of folio_test_idle

Matthew and Gregory, correct me if I am still misunderstanding, man thanks.
> 
> This was THE ENTIRE POINT of Greg's patch.  And why his patch made sense
> and yours is nonsense.  Andrew, please drop this patch series.
>