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Message-Id: <687935F0-EEA5-4CB6-9E5C-43E49FBB39E2@dilger.ca>
Date:	Mon, 11 Jan 2016 14:13:46 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	Lokesh Jaliminche <lokesh.jaliminche@...il.com>,
	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v4] EXT4: optimizing group search for inode allocation

On Jan 6, 2016, at 5:46 PM, Lokesh Jaliminche <lokesh.jaliminche@...il.com> wrote:
> 
> you are right flex groups cannot be completely empty as some
> blocks are used for inode table and allocation bitmaps. I
> missed that point. I have corrected that. Also I have tested
> and validated this patch by putting some traces it works!

Good news.  Thanks for updating the patch and testing it.
More comments below.

> Here are corresponding logs:
> commands:
> =========
> mkfs.ext4 -g 10000 -G 2 /dev/sdc
> mount -t ext4  /dev/sdc /mnt/test_ext4/
> cd /mnt/test_ext4
> mkdir 1
> cd 1
> 
> logs:
> =====
> Jan  7 03:36:45 root kernel: [   64.792939] max_usable_blocks_per_flex_group     =  [19692]
> Jan  7 03:36:45 root kernel: [   64.792939] stats.free_clusters                  =  [19264]
> Jan  7 03:36:45 root kernel: [   64.792939] Inodes_per_flex_group                =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792939] stats.free_inodes                    =  [4853]
> Jan  7 03:36:45 root kernel: [   64.792950] max_usable_blocks_per_flex_group     =  [19692]
> Jan  7 03:36:45 root kernel: [   64.792950] stats.free_clusters                  =  [19481]
> Jan  7 03:36:45 root kernel: [   64.792950] Inodes_per_flex_group                =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792950] stats.free_inodes                    =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792958] max_usable_blocks_per_flex_group     =  [19692]
> Jan  7 03:36:45 root kernel: [   64.792958] stats.free_clusters                  =  [19481]
> Jan  7 03:36:45 root kernel: [   64.792958] Inodes_per_flex_group                =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792958] stats.free_inodes                    =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792965] max_usable_blocks_per_flex_group     =  [19692]
> Jan  7 03:36:45 root kernel: [   64.792965] stats.free_clusters                  =  [19481]
> Jan  7 03:36:45 root kernel: [   64.792965] Inodes_per_flex_group                =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792965] stats.free_inodes                    =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792972] max_usable_blocks_per_flex_group     =  [19692]
> Jan  7 03:36:45 root kernel: [   64.792972] stats.free_clusters                  =  [19481]
> Jan  7 03:36:45 root kernel: [   64.792972] Inodes_per_flex_group                =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792972] stats.free_inodes                    =  [4864]
> Jan  7 03:36:45 root kernel: [   64.792979] max_usable_blocks_per_flex_group     =  [19692]<<<<<<<<<<<
> Jan  7 03:36:45 root kernel: [   64.792979] stats.free_clusters                  =  [19692]<<<<<<<<<<<
> Jan  7 03:36:45 root kernel: [   64.792979] Inodes_per_flex_group                =  [4864]<<<<<<<<<<<<
> Jan  7 03:36:45 root kernel: [   64.792979] stats.free_inodes                    =  [4864]<<<<<<<<<<<<
> Jan  7 03:36:45 root kernel: [   64.792985] found_flex_bg >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>condition satisfied
> 
> 
> [Patch v4]:
> ==========
> From: Lokesh Nagappa Jaliminche <lokesh.jaliminche@...il.com>
> Date: Thu, 7 Jan 2016 05:12:20 +0530
> Subject: [PATCH] ext4: optimizing group serch for inode allocation
> 
> Added a check at the start of group search loop to
> avoid looping unecessarily in case of empty group.
> This also allow group search to jump directly to
> "found_flex_bg" with "stats" and "group" already set,
> so there is no need to go through the extra steps of
> setting "best_desc" , "best_group" and then break
> out of the loop just to set "stats" and "group" again.
> 
> Signed-off-by: Lokesh Nagappa Jaliminche <lokesh.jaliminche@...il.com>
> ---
> fs/ext4/ext4.h   |    2 ++
> fs/ext4/ialloc.c |   21 +++++++++++++++++++--
> 2 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index cc7ca4e..fc48f9a 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -326,6 +326,8 @@ struct flex_groups {
> #define        EXT4_MAX_DESC_SIZE              EXT4_MIN_BLOCK_SIZE
> #define EXT4_DESC_SIZE(s)              (EXT4_SB(s)->s_desc_size)
> #ifdef __KERNEL__
> +# define EXT4_INODE_TABLE_BLOCKS_PER_GROUP(s)  (EXT4_SB(s)->s_itb_per_group)
> +# define EXT4_BLOCKS_PER_CLUSTER(s)    (EXT4_SB(s)->s_cluster_ratio)

I don't think there is much value to these macros.  They aren't much
shorter than the actual variable access, and they don't provide any
improved clarity for the reader.

I think they were introduced many years ago so that this header could
be shared between the kernel and e2fsprogs, but that is no longer true
so I don't think there is a need to add new ones.

Ted, any opinion on this?

> # define EXT4_BLOCKS_PER_GROUP(s)      (EXT4_SB(s)->s_blocks_per_group)
> # define EXT4_CLUSTERS_PER_GROUP(s)    (EXT4_SB(s)->s_clusters_per_group)
> # define EXT4_DESC_PER_BLOCK(s)                (EXT4_SB(s)->s_desc_per_block)
> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> index 1b8024d..dc66ad8 100644
> --- a/fs/ext4/ialloc.c
> +++ b/fs/ext4/ialloc.c
> @@ -463,7 +463,6 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
>                        sbi->s_log_groups_per_flex;
>                parent_group >>= sbi->s_log_groups_per_flex;
>        }
> -
>        freei = percpu_counter_read_positive(&sbi->s_freeinodes_counter);
>        avefreei = freei / ngroups;

Not sure why this line is being deleted?

> @@ -477,7 +476,20 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
>             (ext4_test_inode_flag(parent, EXT4_INODE_TOPDIR)))) {
>                int best_ndir = inodes_per_group;
>                int ret = -1;
> -
> +               /* blocks used for inode table and allocation bitmaps */
> +               unsigned int max_usable_blocks_per_flex_group;

This could be shorter and still clear, like "max_blocks_per_flex".

> +               unsigned int blocks_per_group = EXT4_BLOCKS_PER_GROUP(sb);
> +               unsigned int inode_table_blocks_per_group = \
> +                               EXT4_INODE_TABLE_BLOCKS_PER_GROUP(sb);
> +               /* Number of blocks per cluster */
> +               unsigned int cluster_ratio = EXT4_BLOCKS_PER_CLUSTER(sb);

There also isn't much value to making local variables that hold these
same values again.  It increases stack space for little benefit.  They
are only accessed once anyway.

> +               unsigned int inodes_per_flex_group = inodes_per_group * \
> +                                                       flex_size;
> +               max_usable_blocks_per_flex_group = \
> +                                       ((blocks_per_group*flex_size) - \

Spaces around that '*'.

> +                                       (inode_table_blocks_per_group * \
> +                                       flex_size + 2 * flex_size)) / \

This is C and not a CPP macro, so no need for linefeed escapes.

> +                                       cluster_ratio;

This should be ">> EXT4_SB(sb)->s_cluster_bits" to avoid the divide.

>                if (qstr) {
>                        hinfo.hash_version = DX_HASH_HALF_MD4;
>                        hinfo.seed = sbi->s_hash_seed;
> @@ -489,6 +501,11 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
>                for (i = 0; i < ngroups; i++) {
>                        g = (parent_group + i) % ngroups;
>                        get_orlov_stats(sb, g, flex_size, &stats);
> +                       /* can't get better group than empty group */
> +                       if (max_usable_blocks_per_flex_group == \
> +                               stats.free_clusters && \

No need for linefeed escapes.

> +                               inodes_per_flex_group == stats.free_inodes)

Align continued line after '(' from the "if (" line.

> +                                       goto found_flex_bg;

This is indented too much.  It will work properly when you fix the
previous line.

>                        if (!stats.free_inodes)
>                                continue;
>                        if (stats.used_dirs >= best_ndir)
> --
> 1.7.1
> 
> Regards,
> Lokesh
> 
> On Sun, Jan 03, 2016 at 11:34:51AM -0700, Andreas Dilger wrote:
>> On Dec 26, 2015, at 01:41, Lokesh Jaliminche <lokesh.jaliminche@...il.com> wrote:
>>> 
>>> 
>>> From 5199982d29ff291b181c25af63a22d6f2d6d3f7b Mon Sep 17 00:00:00 2001
>>> From: Lokesh Nagappa Jaliminche <lokesh.jaliminche@...il.com>
>>> Date: Sat, 26 Dec 2015 13:19:36 +0530
>>> Subject: [PATCH v3] ext4: optimizing group search for inode allocation
>>> 
>>> Added a check at the start of group search loop to
>>> avoid looping unecessarily in case of empty group.
>>> This also allow group search to jump directly to
>>> "found_flex_bg" with "stats" and "group" already set,
>>> so there is no need to go through the extra steps of
>>> setting "best_desc" and "best_group" and then break
>>> out of the loop just to set "stats" and "group" again.
>>> 
>>> Signed-off-by: Lokesh Nagappa Jaliminche <lokesh.jaliminche@...il.com>
>>> ---
>>> fs/ext4/ialloc.c |   12 ++++++++++--
>>> 1 files changed, 10 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
>>> index 1b8024d..16f94db 100644
>>> --- a/fs/ext4/ialloc.c
>>> +++ b/fs/ext4/ialloc.c
>>> @@ -473,10 +473,14 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
>>>       ndirs = percpu_counter_read_positive(&sbi->s_dirs_counter);
>>> 
>>>       if (S_ISDIR(mode) &&
>>> -           ((parent == d_inode(sb->s_root)) ||
>>> -            (ext4_test_inode_flag(parent, EXT4_INODE_TOPDIR)))) {
>>> +               ((parent == d_inode(sb->s_root)) ||
>>> +               (ext4_test_inode_flag(parent, EXT4_INODE_TOPDIR)))) {
>> 
>> I don't understand why you are changing the indentation here?
>> 
>>> +               unsigned int inodes_per_flex_group;
>>> +               unsigned long int clusters_per_flex_group;
>>>               int best_ndir = inodes_per_group;
>>>               int ret = -1;
>>> +               inodes_per_flex_group = inodes_per_group * flex_size;
>>> +               clusters_per_flex_group = sbi->s_clusters_per_group * flex_size;
>> 
>> Have you actually tested if this code works?  When I was looking at this
>> code I was accidentally looking at the ext2 version, which only deals with
>> individual groups, and not flex groups.  I don't think that a flex group
>> can actually be completely empty, since it will always contain at least
>> an inode table and some bitmaps.
>> 
>> This calculation needs to take this into account or it will just be
>> overhead and not an optimization. Something like:
>> 
>>                /* account for inode table and allocation bitmaps */
>>                clusters_per_flex_group = sbi->s_clusters_per_group * flex_size -
>>                        ((inodes_per_flex_group * EXT4_INODE_SIZE(sb) +
>>                          (flex_size << sb->s_blocksize_bits) * 2 ) >>
>>                        EXT4_SB(sb)->s_cluster_bits;
>> 
>> It would be worthwhile to print this out and verify that there are actually
>> groups with this many free blocks in a newly formatted filesystem.
>> 
>> Cheers, Andreas
>> 
>>>               if (qstr) {
>>>                       hinfo.hash_version = DX_HASH_HALF_MD4;
>>> @@ -489,6 +493,10 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
>>>               for (i = 0; i < ngroups; i++) {
>>>                       g = (parent_group + i) % ngroups;
>>>                       get_orlov_stats(sb, g, flex_size, &stats);
>>> +                       /* the group can't get any better than empty */
>>> +                       if (inodes_per_flex_group == stats.free_inodes &&
>>> +                               clusters_per_flex_group == stats.free_clusters)
>>> +                               goto found_flex_bg;
>>>                       if (!stats.free_inodes)
>>>                               continue;
>>>                       if (stats.used_dirs >= best_ndir)
>>> --
>>> 1.7.1
>>> 
>>> 
>>>> On Mon, Dec 21, 2015 at 10:27:37AM -0700, Andreas Dilger wrote:
>>>>> On Dec 18, 2015, at 4:32 PM, lokesh jaliminche <lokesh.jaliminche@...il.com> wrote:
>>>>> 
>>>>> From 9e09fef78b2fa552c883bf8124af873abfde0805 Mon Sep 17 00:00:00 2001
>>>>> From: Lokesh Nagappa Jaliminche <lokesh.jaliminche@...gate.com>
>>>> 
>>>> In the patch summary there is a typo - s/serch/search/
>>>> 
>>>> Also, it appears your email client has mangled the whitespace in the
>>>> patch.  Please use "git send-email" to send your patch to the list:
>>>> 
>>>> git send-email --to tytso@....edu --cc linux-ext4@...r.kernel.org HEAD~1
>>>> 
>>>> so that it arrives intact.  You probably need to set it up in ~/.gitconfig:
>>>> 
>>>> [sendemail]
>>>>       confirm = compose
>>>>       smtpdomain = {your client hostname}
>>>>       smtpserver = {your SMTP server hostname}
>>>> 
>>>> Cheers, Andreas
>>>> 
>>>>> Added a check at the start of group search loop to
>>>>> avoid looping unecessarily in case of empty group.
>>>>> This also allow group search to jump directly to
>>>>> "found_flex_bg" with "stats" and "group" already set,
>>>>> so there is no need to go through the extra steps of
>>>>> setting "best_desc" and "best_group" and then break
>>>>> out of the loop just to set "stats" and "group" again.
>>>>> 
>>>>> Signed-off-by: Lokesh N Jaliminche <lokesh.jaliminche@...il.com>
>>>>> ---
>>>>> fs/ext4/ialloc.c |    8 ++++++++
>>>>> 1 files changed, 8 insertions(+), 0 deletions(-)
>>>>> 
>>>>> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
>>>>> index 1b8024d..588bf8e 100644
>>>>> --- a/fs/ext4/ialloc.c
>>>>> +++ b/fs/ext4/ialloc.c
>>>>> @@ -446,6 +446,8 @@ static int find_group_orlov(struct super_block
>>>>> *sb, struct inode *parent,
>>>>> struct ext4_sb_info *sbi = EXT4_SB(sb);
>>>>> ext4_group_t real_ngroups = ext4_get_groups_count(sb);
>>>>> int inodes_per_group = EXT4_INODES_PER_GROUP(sb);
>>>>> + unsigned int inodes_per_flex_group;
>>>>> + long unsigned int blocks_per_clustre;
>>>>> unsigned int freei, avefreei, grp_free;
>>>>> ext4_fsblk_t freeb, avefreec;
>>>>> unsigned int ndirs;
>>>>> @@ -470,6 +472,8 @@ static int find_group_orlov(struct super_block
>>>>> *sb, struct inode *parent,
>>>>> percpu_counter_read_positive(&sbi->s_freeclusters_counter));
>>>>> avefreec = freeb;
>>>>> do_div(avefreec, ngroups);
>>>>> + inodes_per_flex_group = inodes_per_group * flex_size;
>>>>> + blocks_per_clustre = sbi->s_blocks_per_group * flex_size;
>>>>> ndirs = percpu_counter_read_positive(&sbi->s_dirs_counter);
>>>>> 
>>>>> if (S_ISDIR(mode) &&
>>>>> @@ -489,6 +493,10 @@ static int find_group_orlov(struct super_block
>>>>> *sb, struct inode *parent,
>>>>> for (i = 0; i < ngroups; i++) {
>>>>> g = (parent_group + i) % ngroups;
>>>>> get_orlov_stats(sb, g, flex_size, &stats);
>>>>> + /* the group can't get any better than empty */
>>>>> + if (inodes_per_flex_group == stats.free_inodes &&
>>>>> + blocks_per_clustre == stats.free_clusters)
>>>>> + goto found_flex_bg;
>>>>> if (!stats.free_inodes)
>>>>> continue;
>>>>> if (stats.used_dirs >= best_ndir)
>>>>> --
>>>>> 1.7.1
>>>>> <0001-EXT4-optimizing-group-serch-for-inode-allocation.patch>
>>>> 
>>>> 
>>>> Cheers, Andreas
>>> 
>>> 
>>> <0001-ext4-optimizing-group-serch-for-inode-allocation.patch>
> <0001-ext4-optimizing-group-serch-for-inode-allocation.patch>


Cheers, Andreas






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