linux-kernel - Re: [PATCH] erofs: apply proper VMA alignment for memory mapped files on THP

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Date: Wed, 6 Mar 2024 14:51:54 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: linux-erofs@...ts.ozlabs.org
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] erofs: apply proper VMA alignment for memory mapped files
 on THP



On 2024/3/6 13:31, Gao Xiang wrote:
> There are mainly two reasons that thp_get_unmapped_area() should be
> used for EROFS as other filesystems:
> 
>   - It's needed to enable PMD mappings as a FSDAX filesystem, see
>     commit 74d2fad1334d ("thp, dax: add thp_get_unmapped_area for pmd
>     mappings");
> 
>   - It's useful together with CONFIG_READ_ONLY_THP_FOR_FS which enables
>     THPs for read-only mmapped files (e.g. shared libraries) even without
>     FSDAX.  See commit 1854bc6e2420 ("mm/readahead: Align file mappings
>     for non-DAX").

Refine this part as

  - It's useful together with large folios and CONFIG_READ_ONLY_THP_FOR_FS
    which enable THPs for mmapped files (e.g. shared libraries) even without
    ...

> 
> Fixes: 06252e9ce05b ("erofs: dax support for non-tailpacking regular file")

Fixes: ce529cc25b18 ("erofs: enable large folios for iomap mode")
Fixes: be62c5198861 ("erofs: enable large folios for fscache mode")

> Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> ---
>   fs/erofs/data.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index c98aeda8abb2..3d9721b3faa8 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -447,5 +447,6 @@ const struct file_operations erofs_file_fops = {
>   	.llseek		= generic_file_llseek,
>   	.read_iter	= erofs_file_read_iter,
>   	.mmap		= erofs_file_mmap,
> +	.get_unmapped_area = thp_get_unmapped_area,
>   	.splice_read	= filemap_splice_read,
>   };