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. > > > @@ -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 -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
