linux-kernel - Re: [RFC 3/3] block: use mm_huge_zero_folio in __blkdev_issue_zero

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Message-ID: <20250602050514.GD21716@lst.de>
Date: Mon, 2 Jun 2025 07:05:14 +0200
From: Christoph Hellwig <hch@....de>
To: Pankaj Raghav <p.raghav@...sung.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, Zi Yan <ziy@...dia.com>,
	Mike Rapoport <rppt@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Michal Hocko <mhocko@...e.com>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nico Pache <npache@...hat.com>, Dev Jain <dev.jain@....com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-block@...r.kernel.org,
	willy@...radead.org, x86@...nel.org, linux-fsdevel@...r.kernel.org,
	"Darrick J . Wong" <djwong@...nel.org>, mcgrof@...nel.org,
	gost.dev@...sung.com, kernel@...kajraghav.com, hch@....de
Subject: Re: [RFC 3/3] block: use mm_huge_zero_folio in
 __blkdev_issue_zero_pages()

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

> +			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.