Andreas,
we have do it first. But patch was much and much complex due checksums handling in code.
and ext2_flush() will be need to read an all GD in memory to as use a flat array to write a GD to the disk.
If you want we have submit it also, but it have no benefits (like a few seconds), against it simple version.
> 1 марта 2017 г., в 3:10, Andreas Dilger <adilger@xxxxxxxxx> написал(а):
>
> On Feb 20, 2017, at 3:03 AM, Artem Blagodarenko <artem.blagodarenko@xxxxxxxxx> wrote:
>>
>> From: Alexey Lyashkov <alexey.lyashkov@xxxxxxxxxxx>
>>
>> There are ~37k of random IOs with meta_bg option on 300T target.
>> Debugfs requires 20 minutes to be started. Enabling readahead for
>> group blocks metadata save time dramatically. Only 12s to start.
>>
>> Signed-off-by: Alexey Lyashkov <alexey.lyashkov@xxxxxxxxxxx>
>
> This patch looks good by itself.
>
> Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ----
>
> On a related note, I've been wondering if it would make sense to have
> a second patch that *only* does the readahead of the group descriptor blocks
> in ext2fs_open2(), and move io_channel_read_blk64() to ext2fs_group_desc()
> when the group descriptor blocks are actually accessed the first time? This
> would allow tools like tune2fs, debugfs, dumpe2fs, etc. that may not access
> group descriptors to load _much_ faster than if it loads all of the bitmaps
> synchronously at filesystem open time. Even if they _do_ access the GDT it
> will at least allow the prefetch more time to run in the background, and the
> GDT swabbing happen incrementally upon access rather than all at the start.
>
> A quick look through lib/ext2fs looks like ext2fs_group_desc() is used for
> the majority of group descriptor accesses, but there are a few places that
> access fs->group_desc directly. The ext2fs_group_desc() code could check
> whether the group descriptor is all-zero (ext2fs_open2() should be changed
> to use ext2fs_get_array_zero(..., &fs->group_desc)) and if so read the whole
> descriptor block into the array and optionally swab it.
>
> Cheers, Andreas
>
>> ---
>> lib/ext2fs/openfs.c | 6 ++++++
>> 1 files changed, 6 insertions(+), 0 deletions(-)
>>
>> diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
>> index ba501e6..f158b0a 100644
>> --- a/lib/ext2fs/openfs.c
>> +++ b/lib/ext2fs/openfs.c
>> @@ -399,6 +399,12 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
>> #endif
>> dest += fs->blocksize*first_meta_bg;
>> }
>> +
>> + for (i = first_meta_bg ; i < fs->desc_blocks; i++) {
>> + blk = ext2fs_descriptor_block_loc2(fs, group_block, i);
>> + io_channel_cache_readahead(fs->io, blk, 1);
>> + }
>> +
>> for (i=first_meta_bg ; i < fs->desc_blocks; i++) {
>> blk = ext2fs_descriptor_block_loc2(fs, group_block, i);
>> retval = io_channel_read_blk64(fs->io, blk, 1, dest);
>> --
>> 1.7.1
>>
>
>
> Cheers, Andreas
>
>
>
>
>
