patches/kernel/0013-ext4-fallback-to-complex-scan-if-aligned-scan-doesn-.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Ojaswin Mujoo <ojaswin@linux.ibm.com>
   3 Date: Fri, 15 Dec 2023 16:49:50 +0530
   4 Subject: [PATCH] ext4: fallback to complex scan if aligned scan doesn't work
   5
   6 Currently in case the goal length is a multiple of stripe size we use
   7 ext4_mb_scan_aligned() to find the stripe size aligned physical blocks.
   8 In case we are not able to find any, we again go back to calling
   9 ext4_mb_choose_next_group() to search for a different suitable block
  10 group. However, since the linear search always begins from the start,
  11 most of the times we end up with the same BG and the cycle continues.
  12
  13 With large fliesystems, the CPU can be stuck in this loop for hours
  14 which can slow down the whole system. Hence, until we figure out a
  15 better way to continue the search (rather than starting from beginning)
  16 in ext4_mb_choose_next_group(), lets just fallback to
  17 ext4_mb_complex_scan_group() in case aligned scan fails, as it is much
  18 more likely to find the needed blocks.
  19
  20 Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
  21 ---
  22  fs/ext4/mballoc.c | 21 +++++++++++++--------
  23  1 file changed, 13 insertions(+), 8 deletions(-)
  24
  25 diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
  26 index 2690d47a9ea2..9ff8ea02f79d 100644
  27 --- a/fs/ext4/mballoc.c
  28 +++ b/fs/ext4/mballoc.c
  29 @@ -2894,14 +2894,19 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
  30                         ac->ac_groups_scanned++;
  31                         if (cr == CR_POWER2_ALIGNED)
  32                                 ext4_mb_simple_scan_group(ac, &e4b);
  33 -                       else if ((cr == CR_GOAL_LEN_FAST ||
  34 -                                cr == CR_BEST_AVAIL_LEN) &&
  35 -                                sbi->s_stripe &&
  36 -                                !(ac->ac_g_ex.fe_len %
  37 -                                EXT4_B2C(sbi, sbi->s_stripe)))
  38 -                               ext4_mb_scan_aligned(ac, &e4b);
  39 -                       else
  40 -                               ext4_mb_complex_scan_group(ac, &e4b);
  41 +                       else {
  42 +                               bool is_stripe_aligned = sbi->s_stripe &&
  43 +                                       !(ac->ac_g_ex.fe_len %
  44 +                                         EXT4_B2C(sbi, sbi->s_stripe));
  45 +
  46 +                               if ((cr == CR_GOAL_LEN_FAST ||
  47 +                                    cr == CR_BEST_AVAIL_LEN) &&
  48 +                                   is_stripe_aligned)
  49 +                                       ext4_mb_scan_aligned(ac, &e4b);
  50 +
  51 +                               if (ac->ac_status == AC_STATUS_CONTINUE)
  52 +                                       ext4_mb_complex_scan_group(ac, &e4b);
  53 +                       }
  54
  55                         ext4_unlock_group(sb, group);
  56                         ext4_mb_unload_buddy(&e4b);