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Date: Thu, 14 Sep 2023 11:16:25 +0200
From: Jan Kara <jack@...e.cz>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: akpm@...ux-foundation.org, Hui Zhu <teawater@...group.com>,
linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/3] buffer: Hoist GFP flags from grow_dev_page() to
__getblk_gfp()
On Fri 11-08-23 17:15:27, Matthew Wilcox (Oracle) wrote:
> grow_dev_page() is only called by grow_buffers(). grow_buffers()
> is only called by __getblk_slow() and __getblk_slow() is only called
> from __getblk_gfp(), so it is safe to move the GFP flags setting
> all the way up. With that done, add a new bdev_getblk() entry point
> that leaves the GFP flags the way the caller specified them.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Can't we just finish this gfp parameter conversion for all the users?
There are five __getblk_gfp() users, three in buffer_head.h directly
generate gfp mask, two (__bread_gfp() and sb_getblk_gfp()) pass it from the
caller. All three __bread_gfp() callers are in buffer_head.h and directly
generate gfp mask. sb_getblk_gfp() has five callers, all in ext4 and easily
convertable as well.
This results not only in cleaner code but also just checking
sb_getblk_gfp() callers shows how confused they currently are about the gfp
argument (passing NOFS, NOFAIL and other pointless flags). Secondly, we can
keep using sb_getblk_gfp() from the filesystems instead of having to decide
between sb_getblk_gfp() and bdev_getblk().
If you don't have time for this, I guess I can find some...
Honza
> ---
> fs/buffer.c | 60 ++++++++++++++++++++++++-------------
> include/linux/buffer_head.h | 2 ++
> 2 files changed, 41 insertions(+), 21 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 7326acc29541..122b7d16befb 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1048,20 +1048,11 @@ grow_dev_page(struct block_device *bdev, sector_t block,
> struct buffer_head *bh;
> sector_t end_block;
> int ret = 0;
> - gfp_t gfp_mask;
> -
> - gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
> -
> - /*
> - * XXX: __getblk_slow() can not really deal with failure and
> - * will endlessly loop on improvised global reclaim. Prefer
> - * looping in the allocator rather than here, at least that
> - * code knows what it's doing.
> - */
> - gfp_mask |= __GFP_NOFAIL;
>
> folio = __filemap_get_folio(inode->i_mapping, index,
> - FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp_mask);
> + FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp);
> + if (IS_ERR(folio))
> + return PTR_ERR(folio);
>
> bh = folio_buffers(folio);
> if (bh) {
> @@ -1074,7 +1065,9 @@ grow_dev_page(struct block_device *bdev, sector_t block,
> goto failed;
> }
>
> - bh = folio_alloc_buffers(folio, size, gfp_mask);
> + bh = folio_alloc_buffers(folio, size, gfp);
> + if (!bh)
> + goto failed;
>
> /*
> * Link the folio to the buffers and initialise them. Take the
> @@ -1426,24 +1419,49 @@ __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
> }
> EXPORT_SYMBOL(__find_get_block);
>
> +/**
> + * bdev_getblk - Get a buffer_head in a block device's buffer cache.
> + * @bdev: The block device.
> + * @block: The block number.
> + * @size: The size of buffer_heads for this @bdev.
> + * @gfp: The memory allocation flags to use.
> + *
> + * In contrast to __getblk_gfp(), the @gfp flags must be all of the flags;
> + * they are not augmented with the mapping's GFP flags.
> + *
> + * Return: The buffer head, or NULL if memory could not be allocated.
> + */
> +struct buffer_head *bdev_getblk(struct block_device *bdev, sector_t block,
> + unsigned size, gfp_t gfp)
> +{
> + struct buffer_head *bh = __find_get_block(bdev, block, size);
> +
> + might_alloc(gfp);
> + if (bh)
> + return bh;
> +
> + return __getblk_slow(bdev, block, size, gfp);
> +}
> +EXPORT_SYMBOL(bdev_getblk);
> +
> /*
> * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
> * which corresponds to the passed block_device, block and size. The
> * returned buffer has its reference count incremented.
> - *
> - * __getblk_gfp() will lock up the machine if grow_dev_page's
> - * try_to_free_buffers() attempt is failing. FIXME, perhaps?
> */
> struct buffer_head *
> __getblk_gfp(struct block_device *bdev, sector_t block,
> unsigned size, gfp_t gfp)
> {
> - struct buffer_head *bh = __find_get_block(bdev, block, size);
> + gfp |= mapping_gfp_constraint(bdev->bd_inode->i_mapping, ~__GFP_FS);
>
> - might_sleep();
> - if (bh == NULL)
> - bh = __getblk_slow(bdev, block, size, gfp);
> - return bh;
> + /*
> + * Prefer looping in the allocator rather than here, at least that
> + * code knows what it's doing.
> + */
> + gfp |= __GFP_NOFAIL;
> +
> + return bdev_getblk(bdev, block, size, gfp);
> }
> EXPORT_SYMBOL(__getblk_gfp);
>
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index d17efb8b7976..01110db9213c 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -233,6 +233,8 @@ void __wait_on_buffer(struct buffer_head *);
> wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
> struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
> unsigned size);
> +struct buffer_head *bdev_getblk(struct block_device *bdev, sector_t block,
> + unsigned size, gfp_t gfp);
> struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
> unsigned size, gfp_t gfp);
> void __brelse(struct buffer_head *);
> --
> 2.40.1
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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