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

Dmitry Osipenko
2018-01-09T17:03:01Z

On 09.01.2018 17:33, Ming Lei wrote:
> 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,

This patch doesn't help either.