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writeback: allow the file system to override MIN_WRITEBACK_PAGES 

The relatively low minimal writeback size of 4MiB means that written back
inodes on rotational media are switched a lot.  Besides introducing
additional seeks, this also can lead to extreme file fragmentation on
zoned devices when a lot of files are cached relative to the available
writeback bandwidth.

Add a superblock field that allows the file system to override the
default size.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20251017034611.651385-3-hch@lst.de
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christoph Hellwig 2025-10-17 05:45:48 +02:00 committed by Christian Brauner
parent 151d0922bf
commit 90db4d4441
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
4 changed files with 12 additions and 9 deletions
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14
fs/fs-writeback.c
View File

@ -32,11 +32,6 @@
#include <linux/memcontrol.h>
#include "internal.h"
/*
* 4MB minimal write chunk size
*/
#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
/*
* Passed into wb_writeback(), essentially a subset of writeback_control
*/
@ -1889,8 +1884,8 @@ static int writeback_single_inode(struct inode *inode,
return ret;
}
static long writeback_chunk_size(struct bdi_writeback *wb,
struct wb_writeback_work *work)
static long writeback_chunk_size(struct super_block *sb,
struct bdi_writeback *wb, struct wb_writeback_work *work)
{
long pages;
@ -1913,7 +1908,8 @@ static long writeback_chunk_size(struct bdi_writeback *wb,
pages = min(wb->avg_write_bandwidth / 2,
global_wb_domain.dirty_limit / DIRTY_SCOPE);
pages = min(pages, work->nr_pages);
return round_down(pages + MIN_WRITEBACK_PAGES, MIN_WRITEBACK_PAGES);
return round_down(pages + sb->s_min_writeback_pages,
sb->s_min_writeback_pages);
}
/*
@ -2015,7 +2011,7 @@ static long writeback_sb_inodes(struct super_block *sb,
inode->i_state |= I_SYNC;
wbc_attach_and_unlock_inode(&wbc, inode);
write_chunk = writeback_chunk_size(wb, work);
write_chunk = writeback_chunk_size(inode->i_sb, wb, work);
wbc.nr_to_write = write_chunk;
wbc.pages_skipped = 0;

1
fs/super.c
View File

@ -389,6 +389,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
goto fail;
if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink))
goto fail;
s->s_min_writeback_pages = MIN_WRITEBACK_PAGES;
return s;
fail:

1
include/linux/fs.h
View File

@ -1583,6 +1583,7 @@ struct super_block {
spinlock_t s_inode_wblist_lock;
struct list_head s_inodes_wb; /* writeback inodes */
long s_min_writeback_pages;
} __randomize_layout;
static inline struct user_namespace *i_user_ns(const struct inode *inode)

5
include/linux/writeback.h
View File

@ -374,4 +374,9 @@ bool redirty_page_for_writepage(struct writeback_control *, struct page *);
void sb_mark_inode_writeback(struct inode *inode);
void sb_clear_inode_writeback(struct inode *inode);
/*
* 4MB minimal write chunk size
*/
#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
#endif /* WRITEBACK_H */