Eric Sandeen wrote:
> Eric Sandeen wrote:
>> I'll have to think about the right way to do this... it seems pretty
>> convoluted to me right now.
>>
> Something like this probably works, but I really REALLY would not test
> it on an important filesystem. :)
>
> I'm not sure it's a good idea to discard it before returning it
> to the prealloc pool, because it may well get re-used again
> quickly.... not sure if that's helpful.
(now I'm really talking to myself, but scratch that bit -
ext4_mb_return_to_preallocation is pretty much a no-op)
-Eric
> Just a note, I think eventually we may move to more of a batch discard
> in the background, because these little discards are actually quite
> inefficient on the hardware we've tested so far.
>
> -Eric
>
> p.s. really. Don't test this with important data. I haven't tested
> it at all yet.
>
> Index: linux-2.6/fs/ext4/mballoc.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/mballoc.c
> +++ linux-2.6/fs/ext4/mballoc.c
> @@ -4602,6 +4606,8 @@ do_more:
> mb_clear_bits(bitmap_bh->b_data, bit, count);
> ext4_mb_free_metadata(handle, &e4b, new_entry);
> } else {
> + ext4_fsblk_t discard_block;
> +
> /* need to update group_info->bb_free and bitmap
> * with group lock held. generate_buddy look at
> * them with group lock_held
> @@ -4609,6 +4615,11 @@ do_more:
> ext4_lock_group(sb, block_group);
> mb_clear_bits(bitmap_bh->b_data, bit, count);
> mb_free_blocks(inode, &e4b, bit, count);
> + discard_block = bit +
> + ext4_group_first_block_no(sb, block_group);
> + trace_ext4_discard_blocks(sb,
> + (unsigned long long)discard_block, count);
> + sb_issue_discard(sb, discard_block, count);
> ext4_mb_return_to_preallocation(inode, &e4b, block, count);
> }
>
>
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