On 2011-05-05 09:20, Lukas Czerner wrote: > On Mon, 2 May 2011, Jens Axboe wrote: > >> On 2011-05-02 08:17, Lukas Czerner wrote: >>> Currently we are waiting for every submitted REQ_DISCARD bio separately, >>> but it can have unwanted consequences of repeatedly flushing the queue, >>> so we rather submit bios in batches and wait for the entire batch, hence >>> narrowing the window of other ios going in. >>> >>> Use bio_batch_end_io() and struct bio_batch for that purpose, the same >>> is used by blkdev_issue_zeroout(). Also change bio_batch_end_io() so we >>> always set !BIO_UPTODATE in the case of error and remove the check for >>> bb, since we are the only user of this function and we always set this. >>> >>> Remove bio_get()/bio_put() from the blkdev_issue_discard() since >>> bio_alloc() and bio_batch_end_io() is doing the same thing, hence it is >>> not needed anymore. >>> >>> I have done simple dd testing with surprising results. The script I have >>> used is: >>> >>> for i in $(seq 10); do >>> echo $i >>> dd if=/dev/sdb1 of=/dev/sdc1 bs=4k & >>> sleep 5 >>> done >>> /usr/bin/time -f %e ./blkdiscard /dev/sdc1 >>> >>> Running time of BLKDISCARD on the whole device: >>> with patch without patch >>> 0.95 15.58 >>> >>> So we can see that in this artificial test the kernel with the patch >>> applied is approx 16x faster in discarding the device. >> >> Good results. It'd be more efficient to add the vectored discard support >> and use it for this too though, and it would get rid of the need to wait >> on the batches since there'd be just one discard bio for the ranges. >> > > Since we do not have vectored discard yet, can this change go in as it > is ? Also, Christoph thinks that it would not help anyway since the we do > batch the discard requests only when it exceeds the max range. Sure, it need not be a show stopper. I will apply 1-2 for now to for-2.6.40/core. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
