linux-kernel - Re: [PATCH v3 6/7] mm: truncate: split huge page cache page to a non-zero order if possible.

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Message-ID: <86864d6c-39d3-d26f-278f-b96e14884541@google.com>
Date:   Sun, 16 Apr 2023 12:51:46 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Zi Yan <ziy@...dia.com>
cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        linux-mm@...ck.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Michal Koutný <mkoutny@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 6/7] mm: truncate: split huge page cache page to a
 non-zero order if possible.

> As this code stands, truncate a 2M huge page at 1M and you get two 1M
> pieces (one then discarded) - nice; but truncate it at 1M+1 and you get
> lots of order 2 (forced up from 1) pieces.  Seems weird, and not worth
> the effort.

I've probably said that wrong: truncate at 1M+1 and you'd get lots of
order 0 pieces.

Hugh