linux-kernel - Re: [PATCH] f2fs: add a way to change the desired readahead folio order

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Message-ID: <aSALtF5Cty38G2UV@infradead.org>
Date: Thu, 20 Nov 2025 22:50:28 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
	Matthew Wilcox <willy@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] f2fs: add a way to change the desired readahead folio
 order

On Fri, Nov 21, 2025 at 01:48:46AM +0000, Jaegeuk Kim wrote:
> This patch adds a sysfs entry to change the folio order for readahead.

You'll need to explain why this is useful.  And why this is f2fs
specific instead of generic.

> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/data.c  | 1 +
>  fs/f2fs/f2fs.h  | 3 +++
>  fs/f2fs/super.c | 1 +
>  fs/f2fs/sysfs.c | 9 +++++++++
>  4 files changed, 14 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index c80d7960b652..faf1faa27c41 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2764,6 +2764,7 @@ int f2fs_readahead_pages(struct file *file, loff_t offset, loff_t len)
>  	while (nrpages) {
>  		unsigned long this_chunk = min(nrpages, ra_pages);
>  
> +		ractl.ra->desired_order = F2FS_I_SB(inode)->ra_folio_order;
>  		ractl.ra->ra_pages = this_chunk;
>  
>  		page_cache_sync_ra(&ractl, this_chunk << 1);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 934287cc5624..0e61e253d861 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1921,6 +1921,9 @@ struct f2fs_sb_info {
>  	/* carve out reserved_blocks from total blocks */
>  	bool carve_out;
>  
> +	/* enable large folio. */
> +	unsigned int ra_folio_order;
> +
>  #ifdef CONFIG_F2FS_FS_COMPRESSION
>  	struct kmem_cache *page_array_slab;	/* page array entry */
>  	unsigned int page_array_slab_size;	/* default page array slab size */
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index d47ec718f3be..dabac6f288f0 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -4287,6 +4287,7 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
>  			NAT_ENTRY_PER_BLOCK));
>  	sbi->allocate_section_hint = le32_to_cpu(raw_super->section_count);
>  	sbi->allocate_section_policy = ALLOCATE_FORWARD_NOHINT;
> +	sbi->ra_folio_order = 0;
>  	F2FS_ROOT_INO(sbi) = le32_to_cpu(raw_super->root_ino);
>  	F2FS_NODE_INO(sbi) = le32_to_cpu(raw_super->node_ino);
>  	F2FS_META_INO(sbi) = le32_to_cpu(raw_super->meta_ino);
> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index c42f4f979d13..2537a25986a6 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -906,6 +906,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
>  		return count;
>  	}
>  
> +	if (!strcmp(a->attr.name, "ra_folio_order")) {
> +		if (t < 0 || t > MAX_PAGECACHE_ORDER)
> +			return -EINVAL;
> +		sbi->ra_folio_order = t;
> +		return count;
> +	}
> +
>  	*ui = (unsigned int)t;
>  
>  	return count;
> @@ -1180,6 +1187,7 @@ F2FS_SBI_GENERAL_RW_ATTR(migration_window_granularity);
>  F2FS_SBI_GENERAL_RW_ATTR(dir_level);
>  F2FS_SBI_GENERAL_RW_ATTR(allocate_section_hint);
>  F2FS_SBI_GENERAL_RW_ATTR(allocate_section_policy);
> +F2FS_SBI_GENERAL_RW_ATTR(ra_folio_order);
>  #ifdef CONFIG_F2FS_IOSTAT
>  F2FS_SBI_GENERAL_RW_ATTR(iostat_enable);
>  F2FS_SBI_GENERAL_RW_ATTR(iostat_period_ms);
> @@ -1422,6 +1430,7 @@ static struct attribute *f2fs_attrs[] = {
>  	ATTR_LIST(reserved_pin_section),
>  	ATTR_LIST(allocate_section_hint),
>  	ATTR_LIST(allocate_section_policy),
> +	ATTR_LIST(ra_folio_order),
>  	NULL,
>  };
>  ATTRIBUTE_GROUPS(f2fs);
> -- 
> 2.52.0.487.g5c8c507ade-goog
> 
> 
---end quoted text---