linux-kernel - Re: [PATCH 2/2] fs: Do not update nr_thps for mappings which support THPs

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Message-ID: <20200916052126.GA12923@infradead.org>
Date:   Wed, 16 Sep 2020 06:21:26 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Song Liu <songliubraving@...com>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dave Chinner <dchinner@...hat.com>
Subject: Re: [PATCH 2/2] fs: Do not update nr_thps for mappings which support
 THPs

On Wed, Sep 16, 2020 at 04:27:17AM +0100, Matthew Wilcox (Oracle) wrote:
> The nr_thps counter is to support THPs in the page cache when the
> filesystem doesn't understand THPs.  Eventually it will be removed, but
> we should still support filesystems which do not understand THPs yet.
> Move the nr_thp manipulation functions to filemap.h since they're
> page-cache specific.

Honestly I don't think we should support the read-only THP crap.  We
should in fact never have merged that bandaid to start with given that
you did good progress on the real thing.