md/r5cache: read data into orig_page for prexor of cached data

With write back cache, we use orig_page to do prexor. This patch
makes sure we read data into orig_page for it.

Flag R5_OrigPageUPTDODATE is added to show whether orig_page
has the latest data from raid disk.

We introduce a helper function uptodate_for_rmw() to simplify
the a couple conditions in handle_stripe_dirtying().

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index e0d6dd1835d03f031b2dc41e472113997dcee20f..95dcaa022e1f645848fa8796ea95a79258a7821e 100644 (file)
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -2349,6 +2349,8 @@ void r5c_release_extra_page(struct stripe_head *sh)
                        struct page *p = sh->dev[i].orig_page;
 
                        sh->dev[i].orig_page = sh->dev[i].page;
+                       clear_bit(R5_OrigPageUPTDODATE, &sh->dev[i].flags);
+
                        if (!using_disk_info_extra_page)
                                put_page(p);
                }

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 36c13e4be9c9e5d0cedacb59910e7b4482eb6ddd..7780ae44f3559f50c39e93ea7a8b887bb9b0144f 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1015,7 +1015,17 @@ again:
 
                        if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
                                WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
-                       sh->dev[i].vec.bv_page = sh->dev[i].page;
+
+                       if (!op_is_write(op) &&
+                           test_bit(R5_InJournal, &sh->dev[i].flags))
+                               /*
+                                * issuing read for a page in journal, this
+                                * must be preparing for prexor in rmw; read
+                                * the data into orig_page
+                                */
+                               sh->dev[i].vec.bv_page = sh->dev[i].orig_page;
+                       else
+                               sh->dev[i].vec.bv_page = sh->dev[i].page;
                        bi->bi_vcnt = 1;
                        bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                        bi->bi_io_vec[0].bv_offset = 0;
@@ -2380,6 +2390,13 @@ static void raid5_end_read_request(struct bio * bi)
                } else if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
                        clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);
 
+               if (test_bit(R5_InJournal, &sh->dev[i].flags))
+                       /*
+                        * end read for a page in journal, this
+                        * must be preparing for prexor in rmw
+                        */
+                       set_bit(R5_OrigPageUPTDODATE, &sh->dev[i].flags);
+
                if (atomic_read(&rdev->read_errors))
                        atomic_set(&rdev->read_errors, 0);
        } else {
@@ -3594,6 +3611,21 @@ unhash:
                break_stripe_batch_list(head_sh, STRIPE_EXPAND_SYNC_FLAGS);
 }
 
+/*
+ * For RMW in write back cache, we need extra page in prexor to store the
+ * old data. This page is stored in dev->orig_page.
+ *
+ * This function checks whether we have data for prexor. The exact logic
+ * is:
+ *       R5_UPTODATE && (!R5_InJournal || R5_OrigPageUPTDODATE)
+ */
+static inline bool uptodate_for_rmw(struct r5dev *dev)
+{
+       return (test_bit(R5_UPTODATE, &dev->flags)) &&
+               (!test_bit(R5_InJournal, &dev->flags) ||
+                test_bit(R5_OrigPageUPTDODATE, &dev->flags));
+}
+
 static int handle_stripe_dirtying(struct r5conf *conf,
                                  struct stripe_head *sh,
                                  struct stripe_head_state *s,
@@ -3625,9 +3657,7 @@ static int handle_stripe_dirtying(struct r5conf *conf,
                if ((dev->towrite || i == sh->pd_idx || i == sh->qd_idx ||
                     test_bit(R5_InJournal, &dev->flags)) &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
-                   !((test_bit(R5_UPTODATE, &dev->flags) &&
-                      (!test_bit(R5_InJournal, &dev->flags) ||
-                       dev->page != dev->orig_page)) ||
+                   !(uptodate_for_rmw(dev) ||
                      test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rmw++;
@@ -3639,7 +3669,6 @@ static int handle_stripe_dirtying(struct r5conf *conf,
                    i != sh->pd_idx && i != sh->qd_idx &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
-                     test_bit(R5_InJournal, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rcw++;
@@ -3693,9 +3722,7 @@ static int handle_stripe_dirtying(struct r5conf *conf,
                             i == sh->pd_idx || i == sh->qd_idx ||
                             test_bit(R5_InJournal, &dev->flags)) &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
-                           !((test_bit(R5_UPTODATE, &dev->flags) &&
-                              (!test_bit(R5_InJournal, &dev->flags) ||
-                               dev->page != dev->orig_page)) ||
+                           !(uptodate_for_rmw(dev) ||
                              test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (test_bit(STRIPE_PREREAD_ACTIVE,
@@ -3722,7 +3749,6 @@ static int handle_stripe_dirtying(struct r5conf *conf,
                            i != sh->pd_idx && i != sh->qd_idx &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
-                             test_bit(R5_InJournal, &dev->flags) ||
                              test_bit(R5_Wantcompute, &dev->flags))) {
                                rcw++;
                                if (test_bit(R5_Insync, &dev->flags) &&

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index ed8e1362ab3698e6608aceee90614501bb1a69b2..461df197d1572904e962ba462ad50dc9b658dc0b 100644 (file)
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -322,6 +322,11 @@ enum r5dev_flags {
                         * data and parity being written are in the journal
                         * device
                         */
+       R5_OrigPageUPTDODATE,   /* with write back cache, we read old data into
+                                * dev->orig_page for prexor. When this flag is
+                                * set, orig_page contains latest data in the
+                                * raid disk.
+                                */
 };
 
 /*