linux-kernel - Re: [PATCH] f2fs: Use mapping->gfp_mask to get file cache for writing

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Message-ID: <d6609f12-78c2-4a42-b4fd-689b310ec615@kernel.org>
Date: Wed, 24 Sep 2025 10:25:14 +0800
From: Chao Yu <chao@...nel.org>
To: jiucheng.xu@...ogic.com, Jaegeuk Kim <jaegeuk@...nel.org>
Cc: chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org, tuan.zhang@...ogic.com, jianxin.pan@...ogic.com
Subject: Re: [PATCH] f2fs: Use mapping->gfp_mask to get file cache for writing

On 9/18/25 11:32, Jiucheng Xu via B4 Relay wrote:
> From: Jiucheng Xu <jiucheng.xu@...ogic.com>
> 
> On 32-bit architectures, when GFP_NOFS is used, the file cache for write
> operations cannot be allocated from the highmem and CMA.

Hi,

Have you suffered any problem w/o this patch? Can you please describe more
details about it?

> 
> Since mapping->gfp_mask is set to GFP_HIGHUSER_MOVABLE during inode

GFP_HIGHUSER_MOVABLE includes __GFP_FS, we should avoid using __GFP_FS here.
f2fs_write_begin() uses GFP_NOFS like the most of other filesystem to avoid
potential deadlock, as __filemap_get_folio(, .. |__GFP_FS | ..) may run into
memory reclaim to call ->writeback in where we may suffer deadlock potentially.

Thanks,

> allocation, using mapping_gfp_mask(mapping) as the GFP flag of getting file
> cache for writing is more efficient for 32-bit architectures.
> > Signed-off-by: Jiucheng Xu <jiucheng.xu@...ogic.com>
> ---
>  fs/f2fs/data.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 7961e0ddfca3aaa332b7dbd4985ae7766551834f..9fbc41f9accb2626da22754f1a424da4805ca823 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -3587,7 +3587,8 @@ static int f2fs_write_begin(const struct kiocb *iocb,
>  	 * Will wait that below with our IO control.
>  	 */
>  	folio = __filemap_get_folio(mapping, index,
> -				FGP_LOCK | FGP_WRITE | FGP_CREAT, GFP_NOFS);
> +				FGP_LOCK | FGP_WRITE | FGP_CREAT,
> +				mapping_gfp_mask(mapping));
>  	if (IS_ERR(folio)) {
>  		err = PTR_ERR(folio);
>  		goto fail;
> 
> ---
> base-commit: c872b6279cd26762339ff02513e2a3f16149a6f1
> change-id: 20250910-origin-dev-8a5ff6bee1f2
> 
> Best regards,