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

On Mon, Jul 10, 2017 at 11:35:12AM +0800, Ming Lei wrote:

On Mon, Jul 10, 2017 at 7:09 AM, NeilBrown [off-list ref] wrote:

quoted

On Fri, Mar 17 2017, Ming Lei wrote:

quoted

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