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Date:   Sun, 16 Apr 2023 11:11:49 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     Zi Yan <ziy@nvidia.com>, Zi Yan <zi.yan@sent.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Yang Shi <shy828301@gmail.com>, Yu Zhao <yuzhao@google.com>,
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        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        =?ISO-8859-15?Q?Michal_Koutn=FD?= <mkoutny@suse.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Zach O'Keefe <zokeefe@google.com>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 0/7] Split a folio to any lower order folios
In-Reply-To: <20230404144727.e613116684dbd65a4b4745c1@linux-foundation.org>
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References: <20230403201839.4097845-1-zi.yan@sent.com> <20230404144727.e613116684dbd65a4b4745c1@linux-foundation.org>
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On Tue, 4 Apr 2023, Andrew Morton wrote:
> On Mon,  3 Apr 2023 16:18:32 -0400 Zi Yan <zi.yan@sent.com> wrote:
> 
> > File folio supports any order and people would like to support flexible orders
> > for anonymous folio[1] too. Currently, split_huge_page() only splits a huge
> > page to order-0 pages, but splitting to orders higher than 0 is also useful.
> > This patchset adds support for splitting a huge page to any lower order pages
> > and uses it during file folio truncate operations.
> 
> This series (and its v1 & v2) don't appear to have much in the way of
> detailed review.  As it's at v3 and has been fairly stable I'll queue
> it up for some testing now, but I do ask that some reviewers go through
> it please.

Andrew, please don't let this series drift into 6.4-rc1.

I've seen a bug or two (I'll point out in response to those patches),
but overall I don't see what the justification for the series is: done
because it could be done, it seems to me, but liable to add surprises.

The cover letter says "splitting to orders higher than 0 is also useful",
but it's not clear why; and the infrastructure provided seems unsuited
to the one use provided - I'll say more on that truncation patch.

Thanks,
Hugh