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@huawei.com>
---
fs/ext4/ext4.h | 1 -
fs/ext4/mballoc.c | 2 --
2 files changed, 3 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9df74123e7e6..cfb60f8fbb63 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1631,7 +1631,6 @@ struct ext4_sb_info {
unsigned int s_max_dir_size_kb;
/* where last allocation was done - for stream allocation */
unsigned long s_mb_last_group;
- unsigned long s_mb_last_start;
unsigned int s_mb_prefetch;
unsigned int s_mb_prefetch_limit;
unsigned int s_mb_best_avail_max_trim_order;
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 336d65c4f6a2..5cdae3bda072 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2171,7 +2171,6 @@ static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
spin_lock(&sbi->s_md_lock);
sbi->s_mb_last_group = ac->ac_f_ex.fe_group;
- sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
spin_unlock(&sbi->s_md_lock);
}
/*
@@ -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;
spin_unlock(&sbi->s_md_lock);
}
--
2.46.1On 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@huawei.com> 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. Also one nit below but feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> > @@ -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... Honza -- Jan Kara <jack@suse.com> SUSE Labs, CR
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@huawei.com> > 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? > Also one nit below but feel free to add: > > Reviewed-by: Jan Kara <jack@suse.cz> Thanks for your review! > >> @@ -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... > > Honza 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. Thanks, Baokun
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@huawei.com> > > 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@suse.com> SUSE Labs, CR
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@huawei.com> >>> 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
On Mon, Jun 30, 2025 at 03:52:58PM +0800, Baokun Li wrote: > 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@huawei.com> > > > > 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. Hmm idk if giving a sort of one-off special meaning to -1 would be right. How about resetting the original goal group and goal start in the retry logic of ext4_mb_new_blocks()? Since we drop preallocations before retrying, this way we might actually find our goal during the retry (slim chance though but still). Regards, ojaswin > > > Cheers, > Baokun >
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