On Thu 07 Mar 2013 12:23:13 CET, Jan Vesely wrote:
> On Thu 21 Feb 2013 09:30:26 CET, Jan Vesely wrote:
>> 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@xxxxxxxxxx>
>> ---
>> 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
ping?
The described failure is a regression introduced in
46081b166415acb66d4b3150ecefcd9460bb48a1
st: Increase success probability in driver buffer allocation
I have added the signers to cc. I can resend the patch if it is
necessary
thank you,
--
Jan Vesely <jvesely@xxxxxxxxxx>
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