linux-kernel - Re: [PATCH 0/3] mm, thp: introduce a new sysfs interface to facilitate file THP for .text

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Date:   Tue, 12 Oct 2021 02:50:39 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
        song@...nel.org, william.kucharski@...cle.com, hughd@...gle.com,
        shy828301@...il.com, linmiaohe@...wei.com, peterx@...hat.com
Subject: Re: [PATCH 0/3] mm, thp: introduce a new sysfs interface to
 facilitate file THP for .text

On Mon, Oct 11, 2021 at 09:06:37AM +0100, Christoph Hellwig wrote:
> Can we please just get proper pagecache THP (through folios) merged
> instead of piling hacks over hacks here?  The whole readonly THP already
> was more than painful enough due to all the hacks involved.

This was my initial reaction too.

But read the patches.  They're nothing to do with the implementation of
THP / folios in the page cache.  They're all to make sure that mappings
are PMD aligned.

I think there's a lot to criticise in the patches (eg, a system-wide
setting is probably a bad idea.  and a lot of this stuff seems to
be fixing userspace bugs in the kernel).  But let's criticise what's
actually in the patches, because these are problems that exist regardless
of RO_THP vs folios.