Re: [PATCH V4 13/45] block: blk-merge: try to make front segments in full size

Ming Lei
2018-01-09T14:34:08Z

On Tue, Jan 09, 2018 at 04:18:39PM +0300, Dmitry Osipenko wrote:
> 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 <ming.lei@redhat.com>
> >>> ---
> >>> 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

Hi Dmitry,

The 'max_segment_size' of 65535 should be the reason, could you test the
following patch?

---
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 446f63e076aa..38a66e3e678e 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -12,6 +12,8 @@

#include "blk.h"

+#define sector_align(x) ALIGN_DOWN(x, 512)
+
static struct bio *blk_bio_discard_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs,
@@ -109,7 +111,7 @@ 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;
+ int advance = 0;

bio_for_each_segment(bv, bio, iter) {
/*
@@ -144,8 +146,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
* bigger than max segment size, but this
* becomes false after multipage bvecs.
*/
- advance = queue_max_segment_size(q) - seg_size;
-
+ advance = sector_align(
+ queue_max_segment_size(q) -
+ seg_size);
if (advance > 0) {
seg_size += advance;
sectors += advance >> 9;
@@ -386,7 +389,7 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
{

int nbytes = bvec->bv_len;
- unsigned advance = 0;
+ int advance = 0;

if (*sg && *cluster) {
if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
@@ -400,8 +403,9 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
* blk_bio_segment_split()
*/
if ((*sg)->length + nbytes > queue_max_segment_size(q)) {
- advance = queue_max_segment_size(q) - (*sg)->length;
- if (advance) {
+ advance = sector_align(queue_max_segment_size(q) -
+ (*sg)->length);
+ if (advance > 0) {
(*sg)->length += advance;
bvec->bv_offset += advance;
bvec->bv_len -= advance;
@@ -431,12 +435,14 @@ __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 > 0) {
/* 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,

Thanks,
Ming