Re: [patch 3/5] fs: add nofail variant of alloc_buffer_head

Jan Kara
2010-08-24T12:17:49Z

On Tue 24-08-10 03:50:30, David Rientjes wrote:
> Add alloc_buffer_head_nofail(). This function is equivalent to
> alloc_buffer_head(), except that it will never return NULL and instead
> loop forever trying to allocate memory.
>
> If the first allocation attempt fails, a warning will be emitted,
> including a call trace. Subsequent failures will suppress this warning.
>
> This was added as a helper function for documentation and auditability.
> No future callers should be added.
Acked-by: Jan Kara <jack@suse.cz>
for the JBD part here as well.

Honza
>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
> fs/buffer.c | 18 ++++++++++++++++++
> fs/gfs2/log.c | 2 +-
> fs/jbd/journal.c | 2 +-
> include/linux/buffer_head.h | 1 +
> 4 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3238,6 +3238,24 @@ struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
> }
> EXPORT_SYMBOL(alloc_buffer_head);
>
> +/*
> + * NOTE: no new callers of this function should be implemented!
> + * All memory allocations should be failable whenever possible.
> + */
> +struct buffer_head *alloc_buffer_head_nofail(gfp_t gfp_flags)
> +{
> + struct buffer_head *ret;
> +
> + for (;;) {
> + ret = alloc_buffer_head(gfp_flags);
> + if (ret)
> + return ret;
> + WARN_ONCE(1, "Out of memory; no fallback implemented "
> + "(flags=0x%x)\n",
> + gfp_flags);
> + }
> +}
> +
> void free_buffer_head(struct buffer_head *bh)
> {
> BUG_ON(!list_empty(&bh->b_assoc_buffers));
> diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
> --- a/fs/gfs2/log.c
> +++ b/fs/gfs2/log.c
> @@ -523,7 +523,7 @@ struct buffer_head *gfs2_log_fake_buf(struct gfs2_sbd *sdp,
> u64 blkno = log_bmap(sdp, sdp->sd_log_flush_head);
> struct buffer_head *bh;
>
> - bh = alloc_buffer_head(GFP_NOFS | __GFP_NOFAIL);
> + bh = alloc_buffer_head_nofail(GFP_NOFS);
> atomic_set(&bh->b_count, 1);
> bh->b_state = (1 << BH_Mapped) | (1 << BH_Uptodate) | (1 << BH_Lock);
> set_bh_page(bh, real->b_page, bh_offset(real));
> diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
> --- a/fs/jbd/journal.c
> +++ b/fs/jbd/journal.c
> @@ -301,7 +301,7 @@ int journal_write_metadata_buffer(transaction_t *transaction,
> */
> J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));
>
> - new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
> + new_bh = alloc_buffer_head_nofail(GFP_NOFS);
> /* keep subsequent assertions sane */
> new_bh->b_state = 0;
> init_buffer(new_bh, NULL, NULL);
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -176,6 +176,7 @@ void __breadahead(struct block_device *, sector_t block, unsigned int size);
> struct buffer_head *__bread(struct block_device *, sector_t block, unsigned size);
> void invalidate_bh_lrus(void);
> struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
> +struct buffer_head *alloc_buffer_head_nofail(gfp_t gfp_flags);
> void free_buffer_head(struct buffer_head * bh);
> void unlock_buffer(struct buffer_head *bh);
> void __lock_buffer(struct buffer_head *bh);
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR