Messages in this thread Patch in this message | | | Date | Thu, 21 Feb 2013 09:30:26 +0100 | From | Jan Vesely <> | Subject | [PATCH] block: modify __bio_add_page check to accept pages that don't start a new segment |
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The original behavior was to refuse all pages after the maximum number of segments has been reached. However, some drivers (like st) craft their buffers to potentially require exactly max segments and multiple pages in the last segment. This patch modifies the check to allow pages that can be merged into the last segment.
This change fixes EBUSY failures when using large (1mb) tape block size in high memory fragmentation condition.
Signed-off-by: Jan Vesely <jvesely@redhat.com> --- fs/bio.c | 26 ++++++++++++++++---------- 1 files changed, 16 insertions(+), 10 deletions(-)
diff --git a/fs/bio.c b/fs/bio.c index b96fc6c..02efbd5 100644 --- a/fs/bio.c +++ b/fs/bio.c @@ -500,7 +500,6 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page *page, unsigned int len, unsigned int offset, unsigned short max_sectors) { - int retried_segments = 0; struct bio_vec *bvec;
/* @@ -551,18 +550,12 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page return 0;
/* - * we might lose a segment or two here, but rather that than - * make this too complex. + * prepare segment count check, reduce segment count if possible */
- while (bio->bi_phys_segments >= queue_max_segments(q)) { - - if (retried_segments) - return 0; - - retried_segments = 1; + if (bio->bi_phys_segments >= queue_max_segments(q)) blk_recount_segments(q, bio); - } +
/* * setup the new entry, we might clear it again later if we @@ -572,6 +565,19 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page bvec->bv_page = page; bvec->bv_len = len; bvec->bv_offset = offset; + + /* + * the other part of the segment count check, allow mergeable pages + */ + if ((bio->bi_phys_segments > queue_max_segments(q)) || + ( (bio->bi_phys_segments == queue_max_segments(q)) && + !BIOVEC_PHYS_MERGEABLE(bvec - 1, bvec))) { + bvec->bv_page = NULL; + bvec->bv_len = 0; + bvec->bv_offset = 0; + return 0; + } +
/* * if queue has other restrictions (eg varying max sector size -- 1.7.1
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