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authorJens Axboe <jens.axboe@oracle.com>2009-04-15 09:00:07 +0200
committerJens Axboe <jens.axboe@oracle.com>2009-04-15 12:10:12 +0200
commit86c824b9434e764d01489688e4e38aee43b93fcf (patch)
tree0aa776b6fb5af04e9392c3f49842eeee97a5bd74
parent61e0d47c33cc371f725bcda4a47ae0efe652dba8 (diff)
downloadlinaro-lsk-86c824b9434e764d01489688e4e38aee43b93fcf.tar.gz
bio: add documentation to bio_alloc()
Explain that with __GFP_WAIT set it will not fail, and that the caller must never allocate more than 1 bio at the time. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
-rw-r--r--fs/bio.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/fs/bio.c b/fs/bio.c
index e0c9e545bbf..cd42bb882f3 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -348,6 +348,24 @@ err:
return NULL;
}
+/**
+ * bio_alloc - allocate a bio for I/O
+ * @gfp_mask: the GFP_ mask given to the slab allocator
+ * @nr_iovecs: number of iovecs to pre-allocate
+ *
+ * Description:
+ * bio_alloc will allocate a bio and associated bio_vec array that can hold
+ * at least @nr_iovecs entries. Allocations will be done from the
+ * fs_bio_set. Also see @bio_alloc_bioset.
+ *
+ * If %__GFP_WAIT is set, then bio_alloc will always be able to allocate
+ * a bio. This is due to the mempool guarantees. To make this work, callers
+ * must never allocate more than 1 bio at the time from this pool. Callers
+ * that need to allocate more than 1 bio must always submit the previously
+ * allocate bio for IO before attempting to allocate a new one. Failure to
+ * do so can cause livelocks under memory pressure.
+ *
+ **/
struct bio *bio_alloc(gfp_t gfp_mask, int nr_iovecs)
{
struct bio *bio = bio_alloc_bioset(gfp_mask, nr_iovecs, fs_bio_set);