On Tue, May 17, 2011 at 3:57 PM, Andreas Dilger
<adilger.kernel@xxxxxxxxx> wrote:
> On May 17, 2011, at 16:26, Vivek Haldar wrote:
>> The number of hits and misses for each filesystem is exposed in
>> /sys/fs/ext4/<dev>/extent_cache_{hits, misses}.
>
> There was some discussion on the ext4 concall whether the use of the ext4 extent cache is preventing extent and/or index blocks from being "touched", and possibly causing them to be dropped from cache prematurely.
>
> If you are currently investigating this area of the code it would be good if you could take a look at the code to determine if this is the case or not.
I wasn't looking at that issue specifically, but now that you mention
it, I'll keep an eye out for it.
>
>> Tested: fsstress, manual checks.
>> Signed-off-by: Vivek Haldar <haldar@xxxxxxxxxx>
>> ---
>> fs/ext4/ext4.h | 3 +++
>> fs/ext4/extents.c | 7 ++++++-
>> fs/ext4/super.c | 16 ++++++++++++++++
>> 3 files changed, 25 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>> index 47986ae..9625b19 100644
>> --- a/fs/ext4/ext4.h
>> +++ b/fs/ext4/ext4.h
>> @@ -1144,6 +1144,9 @@ struct ext4_sb_info {
>> unsigned long s_ext_blocks;
>> unsigned long s_ext_extents;
>> #endif
>> + /* ext4 extent cache stats */
>> + unsigned long extent_cache_hits;
>> + unsigned long extent_cache_misses;
>>
>> /* for buddy allocator */
>> struct ext4_group_info ***s_group_info;
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index e363f21..1ea440a 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -2035,6 +2035,7 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
>> struct ext4_extent *ex)
>> {
>> struct ext4_ext_cache *cex;
>> + struct ext4_sb_info *sbi;
>> int ret = 0;
>>
>> /*
>> @@ -2042,6 +2043,7 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
>> */
>> spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
>> cex = &EXT4_I(inode)->i_cached_extent;
>> + sbi = EXT4_SB(inode->i_sb);
>>
>> /* has cache valid data? */
>> if (cex->ec_len == 0)
>> @@ -2057,6 +2059,10 @@ ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
>> ret = 1;
>> }
>> errout:
>> + if (!ret)
>> + sbi->extent_cache_misses++;
>> + else
>> + sbi->extent_cache_hits++;
>> spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
>> return ret;
>> }
>> @@ -3900,4 +3906,3 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>>
>> return error;
>> }
>> -
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index fc827bb..20cc98f 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -2439,6 +2439,18 @@ static ssize_t lifetime_write_kbytes_show(struct ext4_attr *a,
>> EXT4_SB(sb)->s_sectors_written_start) >> 1)));
>> }
>>
>> +static ssize_t extent_cache_hits_show(struct ext4_attr *a,
>> + struct ext4_sb_info *sbi, char *buf)
>> +{
>> + return snprintf(buf, PAGE_SIZE, "%lu\n", sbi->extent_cache_hits);
>> +}
>> +
>> +static ssize_t extent_cache_misses_show(struct ext4_attr *a,
>> + struct ext4_sb_info *sbi, char *buf)
>> +{
>> + return snprintf(buf, PAGE_SIZE, "%lu\n", sbi->extent_cache_misses);
>> +}
>> +
>> static ssize_t inode_readahead_blks_store(struct ext4_attr *a,
>> struct ext4_sb_info *sbi,
>> const char *buf, size_t count)
>> @@ -2496,6 +2508,8 @@ static struct ext4_attr ext4_attr_##name = __ATTR(name, mode, show, store)
>> EXT4_RO_ATTR(delayed_allocation_blocks);
>> EXT4_RO_ATTR(session_write_kbytes);
>> EXT4_RO_ATTR(lifetime_write_kbytes);
>> +EXT4_RO_ATTR(extent_cache_hits);
>> +EXT4_RO_ATTR(extent_cache_misses);
>> EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, sbi_ui_show,
>> inode_readahead_blks_store, s_inode_readahead_blks);
>> EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
>> @@ -2511,6 +2525,8 @@ static struct attribute *ext4_attrs[] = {
>> ATTR_LIST(delayed_allocation_blocks),
>> ATTR_LIST(session_write_kbytes),
>> ATTR_LIST(lifetime_write_kbytes),
>> + ATTR_LIST(extent_cache_hits),
>> + ATTR_LIST(extent_cache_misses),
>> ATTR_LIST(inode_readahead_blks),
>> ATTR_LIST(inode_goal),
>> ATTR_LIST(mb_stats),
>> --
>> 1.7.3.1
>>
>
>
> Cheers, Andreas
>
>
>
>
>
>
--
Regards,
Vivek
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