On 2025/6/30 15:31, Jan Kara wrote:
On Mon 30-06-25 11:32:16, Baokun Li wrote:
On 2025/6/28 2:15, Jan Kara wrote:
On Mon 23-06-25 15:32:50, Baokun Li wrote:
ac->ac_g_ex.fe_start is only used in ext4_mb_find_by_goal(), but STREAM
ALLOC is activated after ext4_mb_find_by_goal() fails, so there's no need
to update ac->ac_g_ex.fe_start, remove the unnecessary s_mb_last_start.
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
I'd just note that ac->ac_g_ex.fe_start is also used in
ext4_mb_collect_stats() so this change may impact the statistics gathered
there. OTOH it is questionable whether we even want to account streaming
allocation as a goal hit... Anyway, I'm fine with this, I'd just mention it
in the changelog.
Yes, I missed ext4_mb_collect_stats(). However, instead of explaining
it in the changelog, I think it would be better to move the current
s_bal_goals update to inside or after ext4_mb_find_by_goal().
Then, we could add another variable, such as s_bal_stream_goals, to
represent the hit count for global goals. This kind of statistic would
help us fine-tune the logic for optimizing inode goals and global goals.
What are your thoughts on this?
Sure that sounds good to me.
Ok, I will add a patch to implement that logic in the next version.
@@ -2849,7 +2848,6 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
/* TBD: may be hot point */
spin_lock(&sbi->s_md_lock);
ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
- ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
Maybe reset ac->ac_g_ex.fe_start to 0 instead of leaving it at some random
value? Just for the sake of defensive programming...
ac->ac_g_ex.fe_start holds the inode goal's start position, not a random
value. It's unused after ext4_mb_find_by_goal() (if s_bal_stream_goals is
added). Thus, I see no need for further modification. We can always re-add
it if future requirements change.
Yeah, I was imprecise. It is not a random value. But it is not an offset in
the group we are now setting. Therefore I'd still prefer to reset fe_start
to 0 (or some invalid value like -1 to catch unexpected use).
Honza
When ext4_mb_regular_allocator() fails, it might retry and get called
again. In this scenario, we can't reliably determine if ac_g_ex has
already been modified. Therefore, it might be more appropriate to set
ac_g_ex.fe_start to -1 after ext4_mb_find_by_goal() fails. We can then
skip ext4_mb_find_by_goal() when ac_g_ex.fe_start < 0.
Cheers,
Baokun
