Re: [RFC 3/3] block: use mm_huge_zero_folio in __blkdev_issue_zero_pages()

On 6/2/25 07:05, Christoph Hellwig wrote:

On Tue, May 27, 2025 at 07:04:52AM +0200, Pankaj Raghav wrote:

quoted

Noticed a 4% increase in performance on a commercial NVMe SSD which does
not support OP_WRITE_ZEROES. The device's MDTS was 128K. The performance
gains might be bigger if the device supports bigger MDTS.

Impressive gain on the one hand - on the other hand what is the macro
workload that does a lot of zeroing on an SSD, because avoiding that
should yield even better result while reducing wear..

Absolutely. I think it is better to use either WRITE_ZEROES or DISCARD. But I wanted
to have some measurable workload to show the benefits of using a huge page to zero out.

Interestingly, I have seen many client SSDs not implementing WRITE_ZEROES.

quoted

+			unsigned int len, added = 0;
 
+			len = min_t(sector_t, folio_size(zero_folio),
+				    nr_sects << SECTOR_SHIFT);
+			if (bio_add_folio(bio, zero_folio, len, 0))
+				added = len;
 			if (added < len)
 				break;
 			nr_sects -= added >> SECTOR_SHIFT;

Unless I'm missing something the added variable can go away now, and
the code using it can simply use len.

Yes. This should do it.

if (!bio_add_folio(bio, zero_folio, len, 0))
    break;

nr_sects -= len >> SECTOR_SHIFT;

--
Pankaj