Currently in case if EXT4_MB_GRP_NEED_INIT(grp) is true, then we first
check for few things like grp->bb_free etc with spinlock (ext4_lock_group)
held. Then we drop the lock only to initialize the group's buddy cache
and then again take the lock and check for ext4_mb_good_group().
Once this step is done we return to ext4_mb_regular_allocator(), load
the buddy and then again take the lock only to check
ext4_mb_good_group(), which was anyways done in previous step.
I believe we can optimize one step here where if the group needs init
we can check for only few things and return early. Then recheck for
ext4_mb_good_group() only once after loading the buddy cache.
Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
---
fs/ext4/mballoc.c | 44 +++++++++++++++++++++-----------------------
1 file changed, 21 insertions(+), 23 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index dcd05ff7c012..7d766dc34cdd 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2134,33 +2134,34 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
* during ext4_mb_init_group(). This should not be called with
* ext4_lock_group() held.
*/
-static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
+static bool ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
ext4_group_t group, int cr)
{
struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
struct super_block *sb = ac->ac_sb;
ext4_grpblk_t free;
- int ret = 0;
+ bool ret = false, need_init = EXT4_MB_GRP_NEED_INIT(grp);
ext4_lock_group(sb, group);
- free = grp->bb_free;
- if (free == 0)
- goto out;
- if (cr <= 2 && free < ac->ac_g_ex.fe_len)
- goto out;
- if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
- goto out;
- ext4_unlock_group(sb, group);
-
- /* We only do this if the grp has never been initialized */
- if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
- ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS);
- if (ret)
- return ret;
+ /*
+ * If the group needs init then no need to call ext4_mb_init_group()
+ * after dropping the lock. It's better we check bb_free/other things
+ * here and if it meets the criteria than return true. Later we
+ * will anyway check for good group after loading the buddy cache
+ * which, if required will call ext4_mb_init_group() from within.
+ */
+ if (unlikely(need_init)) {
+ free = grp->bb_free;
+ if (free == 0)
+ goto out;
+ if (cr <= 2 && free < ac->ac_g_ex.fe_len)
+ goto out;
+ if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
+ goto out;
+ ret = true;
+ } else {
+ ret = ext4_mb_good_group(ac, group, cr);
}
-
- ext4_lock_group(sb, group);
- ret = ext4_mb_good_group(ac, group, cr);
out:
ext4_unlock_group(sb, group);
return ret;
@@ -2252,11 +2253,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
/* This now checks without needing the buddy page */
ret = ext4_mb_good_group_nolock(ac, group, cr);
- if (ret <= 0) {
- if (!first_err)
- first_err = ret;
+ if (ret == 0)
continue;
- }
err = ext4_mb_load_buddy(sb, group, &e4b);
if (err)
--
2.21.0
