On 09.01.2018 05:34, Ming Lei wrote: > On Tue, Jan 09, 2018 at 12:09:27AM +0300, Dmitry Osipenko wrote: >> On 18.12.2017 15:22, Ming Lei wrote: >>> When merging one bvec into segment, if the bvec is too big >>> to merge, current policy is to move the whole bvec into another >>> new segment. >>> >>> This patchset changes the policy into trying to maximize size of >>> front segments, that means in above situation, part of bvec >>> is merged into current segment, and the remainder is put >>> into next segment. >>> >>> This patch prepares for support multipage bvec because >>> it can be quite common to see this case and we should try >>> to make front segments in full size. >>> >>> Signed-off-by: Ming Lei <[email protected]> >>> --- >>> block/blk-merge.c | 54 >>> +++++++++++++++++++++++++++++++++++++++++++++++++----- >>> 1 file changed, 49 insertions(+), 5 deletions(-) >>> >>> diff --git a/block/blk-merge.c b/block/blk-merge.c >>> index a476337a8ff4..42ceb89bc566 100644 >>> --- a/block/blk-merge.c >>> +++ b/block/blk-merge.c >>> @@ -109,6 +109,7 @@ static struct bio *blk_bio_segment_split(struct >>> request_queue *q, >>> bool do_split = true; >>> struct bio *new = NULL; >>> const unsigned max_sectors = get_max_io_size(q, bio); >>> + unsigned advance = 0; >>> >>> bio_for_each_segment(bv, bio, iter) { >>> /* >>> @@ -134,12 +135,32 @@ static struct bio *blk_bio_segment_split(struct >>> request_queue *q, >>> } >>> >>> if (bvprvp && blk_queue_cluster(q)) { >>> - if (seg_size + bv.bv_len > queue_max_segment_size(q)) >>> - goto new_segment; >>> if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv)) >>> goto new_segment; >>> if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv)) >>> goto new_segment; >>> + if (seg_size + bv.bv_len > queue_max_segment_size(q)) { >>> + /* >>> + * On assumption is that initial value of >>> + * @seg_size(equals to bv.bv_len) won't be >>> + * bigger than max segment size, but will >>> + * becomes false after multipage bvec comes. >>> + */ >>> + advance = queue_max_segment_size(q) - seg_size; >>> + >>> + if (advance > 0) { >>> + seg_size += advance; >>> + sectors += advance >> 9; >>> + bv.bv_len -= advance; >>> + bv.bv_offset += advance; >>> + } >>> + >>> + /* >>> + * Still need to put remainder of current >>> + * bvec into a new segment. >>> + */ >>> + goto new_segment; >>> + } >>> >>> seg_size += bv.bv_len; >>> bvprv = bv; >>> @@ -161,6 +182,12 @@ static struct bio *blk_bio_segment_split(struct >>> request_queue *q, >>> seg_size = bv.bv_len; >>> sectors += bv.bv_len >> 9; >>> >>> + /* restore the bvec for iterator */ >>> + if (advance) { >>> + bv.bv_len += advance; >>> + bv.bv_offset -= advance; >>> + advance = 0; >>> + } >>> } >>> >>> do_split = false; >>> @@ -361,16 +388,29 @@ __blk_segment_map_sg(struct request_queue *q, struct >>> bio_vec *bvec, >>> { >>> >>> int nbytes = bvec->bv_len; >>> + unsigned advance = 0; >>> >>> if (*sg && *cluster) { >>> - if ((*sg)->length + nbytes > queue_max_segment_size(q)) >>> - goto new_segment; >>> - >>> if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) >>> goto new_segment; >>> if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) >>> goto new_segment; >>> >>> + /* >>> + * try best to merge part of the bvec into previous >>> + * segment and follow same policy with >>> + * blk_bio_segment_split() >>> + */ >>> + if ((*sg)->length + nbytes > queue_max_segment_size(q)) { >>> + advance = queue_max_segment_size(q) - (*sg)->length; >>> + if (advance) { >>> + (*sg)->length += advance; >>> + bvec->bv_offset += advance; >>> + bvec->bv_len -= advance; >>> + } >>> + goto new_segment; >>> + } >>> + >>> (*sg)->length += nbytes; >>> } else { >>> new_segment: >>> @@ -393,6 +433,10 @@ __blk_segment_map_sg(struct request_queue *q, struct >>> bio_vec *bvec, >>> >>> sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset); >>> (*nsegs)++; >>> + >>> + /* for making iterator happy */ >>> + bvec->bv_offset -= advance; >>> + bvec->bv_len += advance; >>> } >>> *bvprv = *bvec; >>> } >>> >> >> Hello, >> >> This patch breaks MMC on next-20180108, in particular MMC doesn't work >> anymore >> with this patch on NVIDIA Tegra20: >> >> <3>[ 36.622253] print_req_error: I/O error, dev mmcblk1, sector 512 >> <3>[ 36.671233] print_req_error: I/O error, dev mmcblk2, sector 128 >> <3>[ 36.711308] print_req_error: I/O error, dev mmcblk1, sector 31325304 >> <3>[ 36.749232] print_req_error: I/O error, dev mmcblk2, sector 512 >> <3>[ 36.761235] print_req_error: I/O error, dev mmcblk1, sector 31325816 >> <3>[ 36.832039] print_req_error: I/O error, dev mmcblk2, sector 31259768 >> <3>[ 99.793248] print_req_error: I/O error, dev mmcblk1, sector 31323136 >> <3>[ 99.982043] print_req_error: I/O error, dev mmcblk1, sector 929792 >> <3>[ 99.986301] print_req_error: I/O error, dev mmcblk1, sector 930816 >> <3>[ 100.293624] print_req_error: I/O error, dev mmcblk1, sector 932864 >> <3>[ 100.466839] print_req_error: I/O error, dev mmcblk1, sector 947200 >> <3>[ 100.642955] print_req_error: I/O error, dev mmcblk1, sector 949248 >> <3>[ 100.818838] print_req_error: I/O error, dev mmcblk1, sector 230400 >> >> Any attempt of mounting MMC block dev ends with a kernel crash. Reverting >> this >> patch fixes the issue. > > Hi Dmitry, > > Thanks for your report! > > Could you share us what the segment limits are on your MMC? > > cat /sys/block/mmcN/queue/max_segment_size > cat /sys/block/mmcN/queue/max_segments > > Please test the following patch to see if your issue can be fixed? > > --- > diff --git a/block/blk-merge.c b/block/blk-merge.c > index 446f63e076aa..cfab36c26608 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -431,12 +431,14 @@ __blk_segment_map_sg(struct request_queue *q, struct > bio_vec *bvec, > > sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset); > (*nsegs)++; > + } > > + *bvprv = *bvec; > + if (advance) { > /* for making iterator happy */ > bvec->bv_offset -= advance; > bvec->bv_len += advance; > } > - *bvprv = *bvec; > } > > static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec > bv,
Hi Ming, I've tried your patch and unfortunately it doesn't help with the issue. Here are the segment limits: # cat /sys/block/mmc*/queue/max_segment_size 65535 65535 65535 65535 # cat /sys/block/mmc*/queue/max_segments 128 128 128 128
