Hi, Yuezhang Mo,
> After traversing all directory entries, hint the empty directory
> entry no matter whether or not there are enough empty directory
> entries.
>
> After this commit, hint the empty directory entries like this:
>
> 1. Hint the deleted directory entries if enough;
> 2. Hint the deleted and unused directory entries which at the
> end of the cluster chain no matter whether enough or not(Add
> by this commit);
> 3. If no any empty directory entries, hint the empty directory
> entries in the new cluster(Add by this commit).
>
> This avoids repeated traversal of directory entries, reduces CPU
> usage, and improves the performance of creating files and
> directories(especially on low-performance CPUs).
>
> Test create 5000 files in a class 4 SD card on imx6q-sabrelite
> with:
>
> for ((i=0;i<5;i++)); do
> sync
> time (for ((j=1;j<=1000;j++)); do touch file$((i*1000+j)); done)
> done
>
> The more files, the more performance improvements.
>
> Before After Improvement
> 1~1000 25.360s 22.168s 14.40%
> 1001~2000 38.242s 28.72ss 33.15%
> 2001~3000 49.134s 35.037s 40.23%
> 3001~4000 62.042s 41.624s 49.05%
> 4001~5000 73.629s 46.772s 57.42%
>
> Signed-off-by: Yuezhang Mo <[email protected]>
> Reviewed-by: Andy Wu <[email protected]>
> Reviewed-by: Aoyama Wataru <[email protected]>
> ---
> fs/exfat/dir.c | 26 ++++++++++++++++++++++----
> fs/exfat/namei.c | 22 ++++++++++++++--------
> 2 files changed, 36 insertions(+), 12 deletions(-)
>
> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
> index a569f285f4fd..7600f3521246 100644
> --- a/fs/exfat/dir.c
> +++ b/fs/exfat/dir.c
> @@ -936,18 +936,25 @@ struct exfat_entry_set_cache
> *exfat_get_dentry_set(struct super_block *sb,
>
> static inline void exfat_hint_empty_entry(struct exfat_inode_info *ei,
> struct exfat_hint_femp *candi_empty, struct exfat_chain *clu,
> - int dentry, int num_entries)
> + int dentry, int num_entries, int entry_type)
> {
> if (ei->hint_femp.eidx == EXFAT_HINT_NONE ||
> ei->hint_femp.count < num_entries ||
> ei->hint_femp.eidx > dentry) {
> + int total_entries = EXFAT_B_TO_DEN(i_size_read(&ei-
> >vfs_inode));
> +
> if (candi_empty->count == 0) {
> candi_empty->cur = *clu;
> candi_empty->eidx = dentry;
> }
>
> - candi_empty->count++;
> - if (candi_empty->count == num_entries)
> + if (entry_type == TYPE_UNUSED)
> + candi_empty->count += total_entries - dentry;
This seems like a very good approach. Perhaps the key fix that improved
performance seems to be the handling of cases where empty space was not
found and ended with TYPE_UNUSED.
However, there are concerns about trusting and using the number of free
entries after TYPE_UNUSED calculated based on directory size. This is
because, unlike exFAT Spec., in the real world, unexpected TYPE_UNUSED
entries may exist. :(
That's why exfat_search_empty_slot() checks if there is any valid entry
after TYPE_UNUSED. In my experience, they can be caused by a wrong FS driver
and H/W defects, and the probability of occurrence is not low.
Therefore, when the lookup ends with TYPE_UNUSED, if there are no empty
entries found yet, it would be better to set the last empty entry to
hint_femp.eidx and set hint_femp.count to 0.
If so, even if the lookup ends with TYPE_UNUSED, exfat_search_empty_slot()
can start searching from the position of the last empty entry and check
whether there are actually empty entries as many as the required
num_entries as now.
what do you think?
> + else
> + candi_empty->count++;
> +
> + if (candi_empty->count == num_entries ||
> + candi_empty->count + candi_empty->eidx == total_entries)
> ei->hint_femp = *candi_empty;
> }
> }
[snip]
> --
> 2.25.1
Add missing Cc: Yuezhang Mo.
2022-10-31 15:17 GMT+09:00, Sungjong Seo <[email protected]>:
> Hi, Yuezhang Mo,
>
>> After traversing all directory entries, hint the empty directory
>> entry no matter whether or not there are enough empty directory
>> entries.
>>
>> After this commit, hint the empty directory entries like this:
>>
>> 1. Hint the deleted directory entries if enough;
>> 2. Hint the deleted and unused directory entries which at the
>> end of the cluster chain no matter whether enough or not(Add
>> by this commit);
>> 3. If no any empty directory entries, hint the empty directory
>> entries in the new cluster(Add by this commit).
>>
>> This avoids repeated traversal of directory entries, reduces CPU
>> usage, and improves the performance of creating files and
>> directories(especially on low-performance CPUs).
>>
>> Test create 5000 files in a class 4 SD card on imx6q-sabrelite
>> with:
>>
>> for ((i=0;i<5;i++)); do
>> sync
>> time (for ((j=1;j<=1000;j++)); do touch file$((i*1000+j)); done)
>> done
>>
>> The more files, the more performance improvements.
>>
>> Before After Improvement
>> 1~1000 25.360s 22.168s 14.40%
>> 1001~2000 38.242s 28.72ss 33.15%
>> 2001~3000 49.134s 35.037s 40.23%
>> 3001~4000 62.042s 41.624s 49.05%
>> 4001~5000 73.629s 46.772s 57.42%
>>
>> Signed-off-by: Yuezhang Mo <[email protected]>
>> Reviewed-by: Andy Wu <[email protected]>
>> Reviewed-by: Aoyama Wataru <[email protected]>
>> ---
>> fs/exfat/dir.c | 26 ++++++++++++++++++++++----
>> fs/exfat/namei.c | 22 ++++++++++++++--------
>> 2 files changed, 36 insertions(+), 12 deletions(-)
>>
>> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
>> index a569f285f4fd..7600f3521246 100644
>> --- a/fs/exfat/dir.c
>> +++ b/fs/exfat/dir.c
>> @@ -936,18 +936,25 @@ struct exfat_entry_set_cache
>> *exfat_get_dentry_set(struct super_block *sb,
>>
>> static inline void exfat_hint_empty_entry(struct exfat_inode_info *ei,
>> struct exfat_hint_femp *candi_empty, struct exfat_chain *clu,
>> - int dentry, int num_entries)
>> + int dentry, int num_entries, int entry_type)
>> {
>> if (ei->hint_femp.eidx == EXFAT_HINT_NONE ||
>> ei->hint_femp.count < num_entries ||
>> ei->hint_femp.eidx > dentry) {
>> + int total_entries = EXFAT_B_TO_DEN(i_size_read(&ei-
>> >vfs_inode));
>> +
>> if (candi_empty->count == 0) {
>> candi_empty->cur = *clu;
>> candi_empty->eidx = dentry;
>> }
>>
>> - candi_empty->count++;
>> - if (candi_empty->count == num_entries)
>> + if (entry_type == TYPE_UNUSED)
>> + candi_empty->count += total_entries - dentry;
>
> This seems like a very good approach. Perhaps the key fix that improved
> performance seems to be the handling of cases where empty space was not
> found and ended with TYPE_UNUSED.
>
> However, there are concerns about trusting and using the number of free
> entries after TYPE_UNUSED calculated based on directory size. This is
> because, unlike exFAT Spec., in the real world, unexpected TYPE_UNUSED
> entries may exist. :(
> That's why exfat_search_empty_slot() checks if there is any valid entry
> after TYPE_UNUSED. In my experience, they can be caused by a wrong FS
> driver
> and H/W defects, and the probability of occurrence is not low.
>
> Therefore, when the lookup ends with TYPE_UNUSED, if there are no empty
> entries found yet, it would be better to set the last empty entry to
> hint_femp.eidx and set hint_femp.count to 0.
> If so, even if the lookup ends with TYPE_UNUSED, exfat_search_empty_slot()
> can start searching from the position of the last empty entry and check
> whether there are actually empty entries as many as the required
> num_entries as now.
>
> what do you think?
>
>> + else
>> + candi_empty->count++;
>> +
>> + if (candi_empty->count == num_entries ||
>> + candi_empty->count + candi_empty->eidx == total_entries)
>> ei->hint_femp = *candi_empty;
>> }
>> }
> [snip]
>> --
>> 2.25.1
>
>
> > This seems like a very good approach. Perhaps the key fix that
> > improved performance seems to be the handling of cases where empty
> > space was not found and ended with TYPE_UNUSED.
> >
> > However, there are concerns about trusting and using the number of
> > free entries after TYPE_UNUSED calculated based on directory size.
> > This is because, unlike exFAT Spec., in the real world, unexpected
> > TYPE_UNUSED entries may exist. :( That's why exfat_search_empty_slot()
> > checks if there is any valid entry after TYPE_UNUSED. In my
> > experience, they can be caused by a wrong FS driver and H/W defects,
> > and the probability of occurrence is not low.
> >
> > Therefore, when the lookup ends with TYPE_UNUSED, if there are no
> > empty entries found yet, it would be better to set the last empty
> > entry to hint_femp.eidx and set hint_femp.count to 0.
> > If so, even if the lookup ends with TYPE_UNUSED,
> > exfat_search_empty_slot() can start searching from the position of the
> > last empty entry and check whether there are actually empty entries as
> > many as the required num_entries as now.
> >
> > what do you think?
We plan to add a new helper exfat_get_empty_dentry_set(), this helper is called before
setting the entry type, it caches and then checks for empty entries(Check-on-write is safer
than checking when looking for empty directory entries).
for (i = 0; i < es->num_entries; i++) {
ep = exfat_get_dentry_cached(es, i);
type = exfat_get_entry_type(ep);
if (type == TYPE_UNUSED)
unused_hit = true;
else if (type == TYPE_DELETED) {
if (unused_hit)
goto error;
} else
goto error;
}
This code is not ready, we are testing and internal reviewing.
> -----Original Message-----
> From: Namjae Jeon <[email protected]>
> Sent: Monday, October 31, 2022 2:32 PM
> To: Sungjong Seo <[email protected]>; Mo, Yuezhang
> <[email protected]>
> Cc: linux-fsdevel <[email protected]>; linux-kernel
> <[email protected]>
> Subject: Re: [PATCH v1 2/2] exfat: hint the empty entry which at the end of
> cluster chain
>
> Add missing Cc: Yuezhang Mo.
>
> 2022-10-31 15:17 GMT+09:00, Sungjong Seo <[email protected]>:
> > Hi, Yuezhang Mo,
> >
> >> After traversing all directory entries, hint the empty directory
> >> entry no matter whether or not there are enough empty directory
> >> entries.
> >>
> >> After this commit, hint the empty directory entries like this:
> >>
> >> 1. Hint the deleted directory entries if enough; 2. Hint the deleted
> >> and unused directory entries which at the
> >> end of the cluster chain no matter whether enough or not(Add
> >> by this commit);
> >> 3. If no any empty directory entries, hint the empty directory
> >> entries in the new cluster(Add by this commit).
> >>
> >> This avoids repeated traversal of directory entries, reduces CPU
> >> usage, and improves the performance of creating files and
> >> directories(especially on low-performance CPUs).
> >>
> >> Test create 5000 files in a class 4 SD card on imx6q-sabrelite
> >> with:
> >>
> >> for ((i=0;i<5;i++)); do
> >> sync
> >> time (for ((j=1;j<=1000;j++)); do touch file$((i*1000+j)); done)
> >> done
> >>
> >> The more files, the more performance improvements.
> >>
> >> Before After Improvement
> >> 1~1000 25.360s 22.168s 14.40%
> >> 1001~2000 38.242s 28.72ss 33.15%
> >> 2001~3000 49.134s 35.037s 40.23%
> >> 3001~4000 62.042s 41.624s 49.05%
> >> 4001~5000 73.629s 46.772s 57.42%
> >>
> >> Signed-off-by: Yuezhang Mo <[email protected]>
> >> Reviewed-by: Andy Wu <[email protected]>
> >> Reviewed-by: Aoyama Wataru <[email protected]>
> >> ---
> >> fs/exfat/dir.c | 26 ++++++++++++++++++++++----
> >> fs/exfat/namei.c | 22 ++++++++++++++--------
> >> 2 files changed, 36 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c index
> >> a569f285f4fd..7600f3521246 100644
> >> --- a/fs/exfat/dir.c
> >> +++ b/fs/exfat/dir.c
> >> @@ -936,18 +936,25 @@ struct exfat_entry_set_cache
> >> *exfat_get_dentry_set(struct super_block *sb,
> >>
> >> static inline void exfat_hint_empty_entry(struct exfat_inode_info *ei,
> >> struct exfat_hint_femp *candi_empty, struct exfat_chain *clu,
> >> - int dentry, int num_entries)
> >> + int dentry, int num_entries, int entry_type)
> >> {
> >> if (ei->hint_femp.eidx == EXFAT_HINT_NONE ||
> >> ei->hint_femp.count < num_entries ||
> >> ei->hint_femp.eidx > dentry) {
> >> + int total_entries = EXFAT_B_TO_DEN(i_size_read(&ei-
> >> >vfs_inode));
> >> +
> >> if (candi_empty->count == 0) {
> >> candi_empty->cur = *clu;
> >> candi_empty->eidx = dentry;
> >> }
> >>
> >> - candi_empty->count++;
> >> - if (candi_empty->count == num_entries)
> >> + if (entry_type == TYPE_UNUSED)
> >> + candi_empty->count += total_entries - dentry;
> >
> > This seems like a very good approach. Perhaps the key fix that
> > improved performance seems to be the handling of cases where empty
> > space was not found and ended with TYPE_UNUSED.
> >
> > However, there are concerns about trusting and using the number of
> > free entries after TYPE_UNUSED calculated based on directory size.
> > This is because, unlike exFAT Spec., in the real world, unexpected
> > TYPE_UNUSED entries may exist. :( That's why exfat_search_empty_slot()
> > checks if there is any valid entry after TYPE_UNUSED. In my
> > experience, they can be caused by a wrong FS driver and H/W defects,
> > and the probability of occurrence is not low.
> >
> > Therefore, when the lookup ends with TYPE_UNUSED, if there are no
> > empty entries found yet, it would be better to set the last empty
> > entry to hint_femp.eidx and set hint_femp.count to 0.
> > If so, even if the lookup ends with TYPE_UNUSED,
> > exfat_search_empty_slot() can start searching from the position of the
> > last empty entry and check whether there are actually empty entries as
> > many as the required num_entries as now.
> >
> > what do you think?
> >
> >> + else
> >> + candi_empty->count++;
> >> +
> >> + if (candi_empty->count == num_entries ||
> >> + candi_empty->count + candi_empty->eidx == total_entries)
> >> ei->hint_femp = *candi_empty;
> >> }
> >> }
> > [snip]
> >> --
> >> 2.25.1
> >
> >
At this stage, we can check this case in exfat_search_empty_slot() by removing the following if statement.
- if (num_entries <= hint_femp->count) {
- hint_femp->eidx = EXFAT_HINT_NONE;
- return dentry;
- }
What do you think?
> -----Original Message-----
> From: Mo, Yuezhang
> Sent: Monday, October 31, 2022 7:05 PM
> To: Namjae Jeon <[email protected]>; Sungjong Seo
> <[email protected]>
> Cc: linux-fsdevel <[email protected]>; linux-kernel
> <[email protected]>
> Subject: RE: [PATCH v1 2/2] exfat: hint the empty entry which at the end of
> cluster chain
>
> > > This seems like a very good approach. Perhaps the key fix that
> > > improved performance seems to be the handling of cases where empty
> > > space was not found and ended with TYPE_UNUSED.
> > >
> > > However, there are concerns about trusting and using the number of
> > > free entries after TYPE_UNUSED calculated based on directory size.
> > > This is because, unlike exFAT Spec., in the real world, unexpected
> > > TYPE_UNUSED entries may exist. :( That's why
> > > exfat_search_empty_slot() checks if there is any valid entry after
> > > TYPE_UNUSED. In my experience, they can be caused by a wrong FS
> > > driver and H/W defects, and the probability of occurrence is not low.
> > >
> > > Therefore, when the lookup ends with TYPE_UNUSED, if there are no
> > > empty entries found yet, it would be better to set the last empty
> > > entry to hint_femp.eidx and set hint_femp.count to 0.
> > > If so, even if the lookup ends with TYPE_UNUSED,
> > > exfat_search_empty_slot() can start searching from the position of
> > > the last empty entry and check whether there are actually empty
> > > entries as many as the required num_entries as now.
> > >
> > > what do you think?
>
> We plan to add a new helper exfat_get_empty_dentry_set(), this helper is
> called before setting the entry type, it caches and then checks for empty
> entries(Check-on-write is safer than checking when looking for empty directory
> entries).
>
> for (i = 0; i < es->num_entries; i++) {
> ep = exfat_get_dentry_cached(es, i);
> type = exfat_get_entry_type(ep);
> if (type == TYPE_UNUSED)
> unused_hit = true;
> else if (type == TYPE_DELETED) {
> if (unused_hit)
> goto error;
> } else
> goto error;
> }
>
> This code is not ready, we are testing and internal reviewing.
>
> > -----Original Message-----
> > From: Namjae Jeon <[email protected]>
> > Sent: Monday, October 31, 2022 2:32 PM
> > To: Sungjong Seo <[email protected]>; Mo, Yuezhang
> > <[email protected]>
> > Cc: linux-fsdevel <[email protected]>; linux-kernel
> > <[email protected]>
> > Subject: Re: [PATCH v1 2/2] exfat: hint the empty entry which at the
> > end of cluster chain
> >
> > Add missing Cc: Yuezhang Mo.
> >
> > 2022-10-31 15:17 GMT+09:00, Sungjong Seo <[email protected]>:
> > > Hi, Yuezhang Mo,
> > >
> > >> After traversing all directory entries, hint the empty directory
> > >> entry no matter whether or not there are enough empty directory
> > >> entries.
> > >>
> > >> After this commit, hint the empty directory entries like this:
> > >>
> > >> 1. Hint the deleted directory entries if enough; 2. Hint the
> > >> deleted and unused directory entries which at the
> > >> end of the cluster chain no matter whether enough or not(Add
> > >> by this commit);
> > >> 3. If no any empty directory entries, hint the empty directory
> > >> entries in the new cluster(Add by this commit).
> > >>
> > >> This avoids repeated traversal of directory entries, reduces CPU
> > >> usage, and improves the performance of creating files and
> > >> directories(especially on low-performance CPUs).
> > >>
> > >> Test create 5000 files in a class 4 SD card on imx6q-sabrelite
> > >> with:
> > >>
> > >> for ((i=0;i<5;i++)); do
> > >> sync
> > >> time (for ((j=1;j<=1000;j++)); do touch file$((i*1000+j)); done)
> > >> done
> > >>
> > >> The more files, the more performance improvements.
> > >>
> > >> Before After Improvement
> > >> 1~1000 25.360s 22.168s 14.40%
> > >> 1001~2000 38.242s 28.72ss 33.15%
> > >> 2001~3000 49.134s 35.037s 40.23%
> > >> 3001~4000 62.042s 41.624s 49.05%
> > >> 4001~5000 73.629s 46.772s 57.42%
> > >>
> > >> Signed-off-by: Yuezhang Mo <[email protected]>
> > >> Reviewed-by: Andy Wu <[email protected]>
> > >> Reviewed-by: Aoyama Wataru <[email protected]>
> > >> ---
> > >> fs/exfat/dir.c | 26 ++++++++++++++++++++++----
> > >> fs/exfat/namei.c | 22 ++++++++++++++--------
> > >> 2 files changed, 36 insertions(+), 12 deletions(-)
> > >>
> > >> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c index
> > >> a569f285f4fd..7600f3521246 100644
> > >> --- a/fs/exfat/dir.c
> > >> +++ b/fs/exfat/dir.c
> > >> @@ -936,18 +936,25 @@ struct exfat_entry_set_cache
> > >> *exfat_get_dentry_set(struct super_block *sb,
> > >>
> > >> static inline void exfat_hint_empty_entry(struct exfat_inode_info *ei,
> > >> struct exfat_hint_femp *candi_empty, struct exfat_chain *clu,
> > >> - int dentry, int num_entries)
> > >> + int dentry, int num_entries, int entry_type)
> > >> {
> > >> if (ei->hint_femp.eidx == EXFAT_HINT_NONE ||
> > >> ei->hint_femp.count < num_entries ||
> > >> ei->hint_femp.eidx > dentry) {
> > >> + int total_entries = EXFAT_B_TO_DEN(i_size_read(&ei-
> > >> >vfs_inode));
> > >> +
> > >> if (candi_empty->count == 0) {
> > >> candi_empty->cur = *clu;
> > >> candi_empty->eidx = dentry;
> > >> }
> > >>
> > >> - candi_empty->count++;
> > >> - if (candi_empty->count == num_entries)
> > >> + if (entry_type == TYPE_UNUSED)
> > >> + candi_empty->count += total_entries - dentry;
> > >
> > > This seems like a very good approach. Perhaps the key fix that
> > > improved performance seems to be the handling of cases where empty
> > > space was not found and ended with TYPE_UNUSED.
> > >
> > > However, there are concerns about trusting and using the number of
> > > free entries after TYPE_UNUSED calculated based on directory size.
> > > This is because, unlike exFAT Spec., in the real world, unexpected
> > > TYPE_UNUSED entries may exist. :( That's why
> > > exfat_search_empty_slot() checks if there is any valid entry after
> > > TYPE_UNUSED. In my experience, they can be caused by a wrong FS
> > > driver and H/W defects, and the probability of occurrence is not low.
> > >
> > > Therefore, when the lookup ends with TYPE_UNUSED, if there are no
> > > empty entries found yet, it would be better to set the last empty
> > > entry to hint_femp.eidx and set hint_femp.count to 0.
> > > If so, even if the lookup ends with TYPE_UNUSED,
> > > exfat_search_empty_slot() can start searching from the position of
> > > the last empty entry and check whether there are actually empty
> > > entries as many as the required num_entries as now.
> > >
> > > what do you think?
> > >
> > >> + else
> > >> + candi_empty->count++;
> > >> +
> > >> + if (candi_empty->count == num_entries ||
> > >> + candi_empty->count + candi_empty->eidx == total_entries)
> > >> ei->hint_femp = *candi_empty;
> > >> }
> > >> }
> > > [snip]
> > >> --
> > >> 2.25.1
> > >
> > >
Hi, Yuezhang,
> At this stage, we can check this case in exfat_search_empty_slot() by
> removing the following if statement.
>
> - if (num_entries <= hint_femp->count) {
> - hint_femp->eidx = EXFAT_HINT_NONE;
> - return dentry;
> - }
>
> What do you think?
Are you planning to remove the code below as well?
+ /* All entries searched but not enough empty entries */
+ if (dentry + hint_femp->count == p_dir->size * dentries_per_clu)
+ return -ENOSPC;
Otherwise, with appropriate comments, it could be modified to:
+ /*
+ * If hint_femp->count is enough, it is needed to check if
+ * there are actual empty entries.
+ * Otherwise, and if "dentry + hint_famp->count" is also equal
+ * to "p_dir->size * dentries_per_clu", it means ENOSPC.
+ */
+ if ((num_entries > hint_femp->count) &&
+ (dentry + hint_femp->count ==
+ p_dir->size * dentries_per_clu))
+ return -ENOSPC;
As of now, it seems like the simplest and the best way.
>
> > -----Original Message-----
> > From: Mo, Yuezhang
> > Sent: Monday, October 31, 2022 7:05 PM
> > To: Namjae Jeon <[email protected]>; Sungjong Seo
> > <[email protected]>
> > Cc: linux-fsdevel <[email protected]>; linux-kernel
> > <[email protected]>
> > Subject: RE: [PATCH v1 2/2] exfat: hint the empty entry which at the
> > end of cluster chain
> >
> > > > This seems like a very good approach. Perhaps the key fix that
> > > > improved performance seems to be the handling of cases where empty
> > > > space was not found and ended with TYPE_UNUSED.
> > > >
> > > > However, there are concerns about trusting and using the number of
> > > > free entries after TYPE_UNUSED calculated based on directory size.
> > > > This is because, unlike exFAT Spec., in the real world, unexpected
> > > > TYPE_UNUSED entries may exist. :( That's why
> > > > exfat_search_empty_slot() checks if there is any valid entry after
> > > > TYPE_UNUSED. In my experience, they can be caused by a wrong FS
> > > > driver and H/W defects, and the probability of occurrence is not low.
> > > >
> > > > Therefore, when the lookup ends with TYPE_UNUSED, if there are no
> > > > empty entries found yet, it would be better to set the last empty
> > > > entry to hint_femp.eidx and set hint_femp.count to 0.
> > > > If so, even if the lookup ends with TYPE_UNUSED,
> > > > exfat_search_empty_slot() can start searching from the position of
> > > > the last empty entry and check whether there are actually empty
> > > > entries as many as the required num_entries as now.
> > > >
> > > > what do you think?
> >
> > We plan to add a new helper exfat_get_empty_dentry_set(), this helper
> > is called before setting the entry type, it caches and then checks for
> > empty entries(Check-on-write is safer than checking when looking for
> > empty directory entries).
> >
> > for (i = 0; i < es->num_entries; i++) {
> > ep = exfat_get_dentry_cached(es, i);
> > type = exfat_get_entry_type(ep);
> > if (type == TYPE_UNUSED)
> > unused_hit = true;
> > else if (type == TYPE_DELETED) {
> > if (unused_hit)
> > goto error;
> > } else
> > goto error;
> > }
> >
> > This code is not ready, we are testing and internal reviewing.
> >
> > > -----Original Message-----
> > > From: Namjae Jeon <[email protected]>
> > > Sent: Monday, October 31, 2022 2:32 PM
> > > To: Sungjong Seo <[email protected]>; Mo, Yuezhang
> > > <[email protected]>
> > > Cc: linux-fsdevel <[email protected]>; linux-kernel
> > > <[email protected]>
> > > Subject: Re: [PATCH v1 2/2] exfat: hint the empty entry which at the
> > > end of cluster chain
> > >
> > > Add missing Cc: Yuezhang Mo.
> > >
> > > 2022-10-31 15:17 GMT+09:00, Sungjong Seo <[email protected]>:
> > > > Hi, Yuezhang Mo,
> > > >
> > > >> After traversing all directory entries, hint the empty directory
> > > >> entry no matter whether or not there are enough empty directory
> > > >> entries.
> > > >>
> > > >> After this commit, hint the empty directory entries like this:
> > > >>
> > > >> 1. Hint the deleted directory entries if enough; 2. Hint the
> > > >> deleted and unused directory entries which at the
> > > >> end of the cluster chain no matter whether enough or not(Add
> > > >> by this commit);
> > > >> 3. If no any empty directory entries, hint the empty directory
> > > >> entries in the new cluster(Add by this commit).
> > > >>
> > > >> This avoids repeated traversal of directory entries, reduces CPU
> > > >> usage, and improves the performance of creating files and
> > > >> directories(especially on low-performance CPUs).
> > > >>
> > > >> Test create 5000 files in a class 4 SD card on imx6q-sabrelite
> > > >> with:
> > > >>
> > > >> for ((i=0;i<5;i++)); do
> > > >> sync
> > > >> time (for ((j=1;j<=1000;j++)); do touch file$((i*1000+j));
> > > >> done) done
> > > >>
> > > >> The more files, the more performance improvements.
> > > >>
> > > >> Before After Improvement
> > > >> 1~1000 25.360s 22.168s 14.40%
> > > >> 1001~2000 38.242s 28.72ss 33.15%
> > > >> 2001~3000 49.134s 35.037s 40.23%
> > > >> 3001~4000 62.042s 41.624s 49.05%
> > > >> 4001~5000 73.629s 46.772s 57.42%
> > > >>
> > > >> Signed-off-by: Yuezhang Mo <[email protected]>
> > > >> Reviewed-by: Andy Wu <[email protected]>
> > > >> Reviewed-by: Aoyama Wataru <[email protected]>
> > > >> ---
> > > >> fs/exfat/dir.c | 26 ++++++++++++++++++++++----
> > > >> fs/exfat/namei.c | 22 ++++++++++++++--------
> > > >> 2 files changed, 36 insertions(+), 12 deletions(-)
> > > >>
> > > >> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c index
> > > >> a569f285f4fd..7600f3521246 100644
> > > >> --- a/fs/exfat/dir.c
> > > >> +++ b/fs/exfat/dir.c
> > > >> @@ -936,18 +936,25 @@ struct exfat_entry_set_cache
> > > >> *exfat_get_dentry_set(struct super_block *sb,
> > > >>
> > > >> static inline void exfat_hint_empty_entry(struct exfat_inode_info
> *ei,
> > > >> struct exfat_hint_femp *candi_empty, struct
> exfat_chain *clu,
> > > >> - int dentry, int num_entries)
> > > >> + int dentry, int num_entries, int entry_type)
> > > >> {
> > > >> if (ei->hint_femp.eidx == EXFAT_HINT_NONE ||
> > > >> ei->hint_femp.count < num_entries ||
> > > >> ei->hint_femp.eidx > dentry) {
> > > >> + int total_entries = EXFAT_B_TO_DEN(i_size_read(&ei-
> > > >> >vfs_inode));
> > > >> +
> > > >> if (candi_empty->count == 0) {
> > > >> candi_empty->cur = *clu;
> > > >> candi_empty->eidx = dentry;
> > > >> }
> > > >>
> > > >> - candi_empty->count++;
> > > >> - if (candi_empty->count == num_entries)
> > > >> + if (entry_type == TYPE_UNUSED)
> > > >> + candi_empty->count += total_entries - dentry;
> > > >
> > > > This seems like a very good approach. Perhaps the key fix that
> > > > improved performance seems to be the handling of cases where empty
> > > > space was not found and ended with TYPE_UNUSED.
> > > >
> > > > However, there are concerns about trusting and using the number of
> > > > free entries after TYPE_UNUSED calculated based on directory size.
> > > > This is because, unlike exFAT Spec., in the real world, unexpected
> > > > TYPE_UNUSED entries may exist. :( That's why
> > > > exfat_search_empty_slot() checks if there is any valid entry after
> > > > TYPE_UNUSED. In my experience, they can be caused by a wrong FS
> > > > driver and H/W defects, and the probability of occurrence is not low.
> > > >
> > > > Therefore, when the lookup ends with TYPE_UNUSED, if there are no
> > > > empty entries found yet, it would be better to set the last empty
> > > > entry to hint_femp.eidx and set hint_femp.count to 0.
> > > > If so, even if the lookup ends with TYPE_UNUSED,
> > > > exfat_search_empty_slot() can start searching from the position of
> > > > the last empty entry and check whether there are actually empty
> > > > entries as many as the required num_entries as now.
> > > >
> > > > what do you think?
> > > >
> > > >> + else
> > > >> + candi_empty->count++;
> > > >> +
> > > >> + if (candi_empty->count == num_entries ||
> > > >> + candi_empty->count + candi_empty->eidx ==
> total_entries)
> > > >> ei->hint_femp = *candi_empty;
> > > >> }
> > > >> }
> > > > [snip]
> > > >> --
> > > >> 2.25.1
> > > >
> > > >