linux-kernel - Re: [PATCH 09/12] mm/readahead: Align file mappings for non-DAX

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Message-ID: <YeTzQU+JR43x6kha@casper.infradead.org>
Date:   Mon, 17 Jan 2022 04:40:33 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        William Kucharski <william.kucharski@...cle.com>
Subject: Re: [PATCH 09/12] mm/readahead: Align file mappings for non-DAX

On Mon, Jan 17, 2022 at 11:17:55AM +0800, Rongwei Wang wrote:
> It seems this patch will make all file mappings align with PMD_SIZE?

Only those which are big enough.  See __thp_get_unmapped_area():

        if (off_end <= off_align || (off_end - off_align) < size)
                return 0;

> And
> support realize all file THP, not only executable file THP?

Executables are not the only files which benefit from being mapped
to an aligned address.  If you can use a PMD to map a font file,
for example, that's valuable.