ext4: Ensure ext4_mb_prefetch_fini() is called for all prefetched BGs

Before this patch, the call stack in ext4_run_li_request is as follows:

  /*
   * nr = no. of BGs we want to fetch (=s_mb_prefetch)
   * prefetch_ios = no. of BGs not uptodate after
   * 		    ext4_read_block_bitmap_nowait()
   */
  next_group = ext4_mb_prefetch(sb, group, nr, prefetch_ios);
  ext4_mb_prefetch_fini(sb, next_group prefetch_ios);

ext4_mb_prefetch_fini() will only try to initialize buddies for BGs in
range [next_group - prefetch_ios, next_group). This is incorrect since
sometimes (prefetch_ios < nr), which causes ext4_mb_prefetch_fini() to
incorrectly ignore some of the BGs that might need initialization. This
issue is more notable now with the previous patch enabling "fetching" of
BLOCK_UNINIT BGs which are marked buffer_uptodate by default.

Fix this by passing nr to ext4_mb_prefetch_fini() instead of
prefetch_ios so that it considers the right range of groups.

Similarly, make sure we don't pass nr=0 to ext4_mb_prefetch_fini() in
ext4_mb_regular_allocator() since we might have prefetched BLOCK_UNINIT
groups that would need buddy initialization.

Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/05e648ae04ec5b754207032823e9c1de9a54f87a.1685449706.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index fb9780b..d2a0259 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2734,8 +2734,6 @@ repeat:
                        if ((prefetch_grp == group) &&
                            (cr > CR1 ||
                             prefetch_ios < sbi->s_mb_prefetch_limit)) {
-                               unsigned int curr_ios = prefetch_ios;
-
                                nr = sbi->s_mb_prefetch;
                                if (ext4_has_feature_flex_bg(sb)) {
                                        nr = 1 << sbi->s_log_groups_per_flex;
@@ -2744,8 +2742,6 @@ repeat:
                                }
                                prefetch_grp = ext4_mb_prefetch(sb, group,
                                                        nr, &prefetch_ios);
-                               if (prefetch_ios == curr_ios)
-                                       nr = 0;
                        }
 
                        /* This now checks without needing the buddy page */

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 39591fb..7f9b087 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3692,16 +3692,13 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
        ext4_group_t group = elr->lr_next_group;
        unsigned int prefetch_ios = 0;
        int ret = 0;
+       int nr = EXT4_SB(sb)->s_mb_prefetch;
        u64 start_time;
 
        if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) {
-               elr->lr_next_group = ext4_mb_prefetch(sb, group,
-                               EXT4_SB(sb)->s_mb_prefetch, &prefetch_ios);
-               if (prefetch_ios)
-                       ext4_mb_prefetch_fini(sb, elr->lr_next_group,
-                                             prefetch_ios);
-               trace_ext4_prefetch_bitmaps(sb, group, elr->lr_next_group,
-                                           prefetch_ios);
+               elr->lr_next_group = ext4_mb_prefetch(sb, group, nr, &prefetch_ios);
+               ext4_mb_prefetch_fini(sb, elr->lr_next_group, nr);
+               trace_ext4_prefetch_bitmaps(sb, group, elr->lr_next_group, nr);
                if (group >= elr->lr_next_group) {
                        ret = 1;
                        if (elr->lr_first_not_zeroed != ngroups &&