> 28 февр. 2017 г., в 19:19, Darrick J. Wong <darrick.wong@xxxxxxxxxx> написал(а):
>
> On Mon, Feb 20, 2017 at 07:45:53PM +0300, Artem Blagodarenko wrote:
>> From: Andrew Perepechko <andrew.perepechko@xxxxxxxxxxx>
>>
>> With enabled meta_bg option block group descriptors
>> reading IO is not sequential and requires optimization.
>>
>> Signed-off-by: Andrew Perepechko <andrew.perepechko@xxxxxxxxxxx>
>> ---
>> fs/ext4/super.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index a673558..0e52c91 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -3879,6 +3879,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>>
>> bgl_lock_init(sbi->s_blockgroup_lock);
>>
>> + /* Pre-read the descriptors into the buffer cache */
>> + for (i = 0; i < db_count; i++) {
>> + block = descriptor_loc(sb, logical_sb_block, i);
>> + sb_breadahead(sb, block);
>> + }
>
> Why does the libext2fs patch start readahead only on the meta bgs
> whereas this patch starts it for all of them? I suppose it's just as
> well that the kernel prefetches all of them, but I was curious. :)
>
Just because a simplify code.
libext2fs makes read a first gd porting via single read call, it fast.
while just meta_bg generate a random io load.
while a kernel part just a copy/paste a second loop :) Artem have a modified version for this patch,
when sb_bread_unmovable moved into ext4_check_descriptors to have chance increase window between read-ahead call and access to the buffer.
What about such change?
> --D
>
>> +
>> for (i = 0; i < db_count; i++) {
>> block = descriptor_loc(sb, logical_sb_block, i);
>> sbi->s_group_desc[i] = sb_bread_unmovable(sb, block);
>> --
>> 1.8.3.1
