Re: [PATCH v3 05/14] md: raid1: don't use bio's vec table to manage resync pages

Ming Lei
2017-07-10T04:13:28Z

On Mon, Jul 10, 2017 at 11:35:12AM +0800, Ming Lei wrote:
> On Mon, Jul 10, 2017 at 7:09 AM, NeilBrown <neilb@suse.com> wrote:
> > On Fri, Mar 17 2017, Ming Lei wrote:
> >
> >> Now we allocate one page array for managing resync pages, instead
> >> of using bio's vec table to do that, and the old way is very hacky
> >> and won't work any more if multipage bvec is enabled.
> >>
> >> The introduced cost is that we need to allocate (128 + 16) * raid_disks
> >> bytes per r1_bio, and it is fine because the inflight r1_bio for
> >> resync shouldn't be much, as pointed by Shaohua.
> >>
> >> Also the bio_reset() in raid1_sync_request() is removed because
> >> all bios are freshly new now and not necessary to reset any more.
> >>
> >> This patch can be thought as a cleanup too
> >>
> >> Suggested-by: Shaohua Li <shli@kernel.org>
> >> Signed-off-by: Ming Lei <tom.leiming@gmail.com>
> >> ---
> >> drivers/md/raid1.c | 94 +++++++++++++++++++++++++++++++++++++-----------------
> >> 1 file changed, 64 insertions(+), 30 deletions(-)
> >>
> >> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> >> index e30d89690109..0e64beb60e4d 100644
> >> --- a/drivers/md/raid1.c
> >> +++ b/drivers/md/raid1.c
> >> @@ -80,6 +80,24 @@ static void lower_barrier(struct r1conf *conf, sector_t sector_nr);
> >> #define raid1_log(md, fmt, args...) \
> >> do { if ((md)->queue) blk_add_trace_msg((md)->queue, "raid1 " fmt, ##args); } while (0)
> >>
> >> +/*
> >> + * 'strct resync_pages' stores actual pages used for doing the resync
> >> + * IO, and it is per-bio, so make .bi_private points to it.
> >> + */
> >> +static inline struct resync_pages *get_resync_pages(struct bio *bio)
> >> +{
> >> + return bio->bi_private;
> >> +}
> >> +
> >> +/*
> >> + * for resync bio, r1bio pointer can be retrieved from the per-bio
> >> + * 'struct resync_pages'.
> >> + */
> >> +static inline struct r1bio *get_resync_r1bio(struct bio *bio)
> >> +{
> >> + return get_resync_pages(bio)->raid_bio;
> >> +}
> >> +
> >> static void * r1bio_pool_alloc(gfp_t gfp_flags, void *data)
> >> {
> >> struct pool_info *pi = data;
> >> @@ -107,12 +125,18 @@ static void * r1buf_pool_alloc(gfp_t gfp_flags, void *data)
> >> struct r1bio *r1_bio;
> >> struct bio *bio;
> >> int need_pages;
> >> - int i, j;
> >> + int j;
> >> + struct resync_pages *rps;
> >>
> >> r1_bio = r1bio_pool_alloc(gfp_flags, pi);
> >> if (!r1_bio)
> >> return NULL;
> >>
> >> + rps = kmalloc(sizeof(struct resync_pages) * pi->raid_disks,
> >> + gfp_flags);
> >> + if (!rps)
> >> + goto out_free_r1bio;
> >> +
> >> /*
> >> * Allocate bios : 1 for reading, n-1 for writing
> >> */
> >> @@ -132,22 +156,22 @@ static void * r1buf_pool_alloc(gfp_t gfp_flags, void *data)
> >> need_pages = pi->raid_disks;
> >> else
> >> need_pages = 1;
> >> - for (j = 0; j < need_pages; j++) {
> >> + for (j = 0; j < pi->raid_disks; j++) {
> >> + struct resync_pages *rp = &rps[j];
> >> +
> >> bio = r1_bio->bios[j];
> >> - bio->bi_vcnt = RESYNC_PAGES;
> >> -
> >> - if (bio_alloc_pages(bio, gfp_flags))
> >> - goto out_free_pages;
> >> - }
> >> - /* If not user-requests, copy the page pointers to all bios */
> >> - if (!test_bit(MD_RECOVERY_REQUESTED, &pi->mddev->recovery)) {
> >> - for (i=0; i<RESYNC_PAGES ; i++)
> >> - for (j=1; j<pi->raid_disks; j++) {
> >> - struct page *page =
> >> - r1_bio->bios[0]->bi_io_vec[i].bv_page;
> >> - get_page(page);
> >> - r1_bio->bios[j]->bi_io_vec[i].bv_page = page;
> >> - }
> >> +
> >> + if (j < need_pages) {
> >> + if (resync_alloc_pages(rp, gfp_flags))
> >> + goto out_free_pages;
> >> + } else {
> >> + memcpy(rp, &rps[0], sizeof(*rp));
> >> + resync_get_all_pages(rp);
> >> + }
> >> +
> >> + rp->idx = 0;
> >
> > This is the only place the ->idx is initialized, in r1buf_pool_alloc().
> > The mempool alloc function is suppose to allocate memory, not initialize
> > it.
> >
> > If the mempool_alloc() call cannot allocate memory it will use memory
> > from the pool. If this memory has already been used, then it will no
> > longer have the initialized value.
> >
> > In short: you need to initialise memory *after* calling
> > mempool_alloc(), unless you ensure it is reset to the init values before
> > calling mempool_free().
> >
> > https://bugzilla.kernel.org/show_bug.cgi?id=196307
>
> OK, thanks for posting it out.
>
> Another fix might be to reinitialize the variable(rp->idx = 0) in
> r1buf_pool_free().
> Or just set it as zero every time when it is used.
>
> But I don't understand why mempool_free() calls pool->free() at the end of
> this function, which may cause to run pool->free() on a new allocated buf,
> seems a bug in mempool?

Looks I missed the 'return' in mempool_free(), so it is fine.

How about the following fix?

---
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index e1a7e3d4c5e4..d31b06da3e3d 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -242,6 +242,7 @@ static void put_buf(struct r1bio *r1_bio)
struct bio *bio = r1_bio->bios[i];
if (bio->bi_end_io)
rdev_dec_pending(conf->mirrors[i].rdev, r1_bio->mddev);
+ get_resync_pages(bio)->idx = 0;
}

mempool_free(r1_bio, conf->r1buf_pool);
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 797ed60abd5e..c61523768745 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -299,12 +299,21 @@ static void free_r10bio(struct r10bio *r10_bio)
mempool_free(r10_bio, conf->r10bio_pool);
}

-static void put_buf(struct r10bio *r10_bio)
+static void free_r10bio_buf(struct r10bio *r10_bio, struct r10conf *conf)
{
- struct r10conf *conf = r10_bio->mddev->private;
+ int j;
+
+ for (j = conf->copies; j--; )
+ get_resync_pages(r10_bio->devs[j].bio)->idx = 0;

mempool_free(r10_bio, conf->r10buf_pool);
+}
+
+static void put_buf(struct r10bio *r10_bio)
+{
+ struct r10conf *conf = r10_bio->mddev->private;

+ free_r10bio_buf(r10_bio, conf);
lower_barrier(conf);
}

@@ -4383,7 +4392,7 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
* on all the target devices.
*/
// FIXME
- mempool_free(r10_bio, conf->r10buf_pool);
+ free_r10bio_buf(r10_bio, conf);
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
return sectors_done;
}

--
Ming