Received-SPF: pass (google.com: domain of linux-kernel+bounces-160878-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Date: Sat, 27 Apr 2024 04:26:44 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>, djwong@kernel.org,
	brauner@kernel.org, david@fromorbit.com, chandan.babu@oracle.com,
	akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
	hare@suse.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-xfs@vger.kernel.org, mcgrof@kernel.org, gost.dev@samsung.com,
	p.raghav@samsung.com
Subject: Re: [PATCH v4 07/11] iomap: fix iomap_dio_zero() for fs bs > system
 page size
Message-ID: <ZixwdKxqYWq4-rxd@casper.infradead.org>
References: <20240425113746.335530-1-kernel@pankajraghav.com>
 <20240425113746.335530-8-kernel@pankajraghav.com>
 <ZitIK5OnR7ZNY0IG@infradead.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ZitIK5OnR7ZNY0IG@infradead.org>

On Thu, Apr 25, 2024 at 11:22:35PM -0700, Christoph Hellwig wrote:
> On Thu, Apr 25, 2024 at 01:37:42PM +0200, Pankaj Raghav (Samsung) wrote:
> > From: Pankaj Raghav <p.raghav@samsung.com>
> > 
> > iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> > < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> > size < page_size. This is true for most filesystems at the moment.
> > 
> > If the block size > page size, this will send the contents of the page
> > next to zero page(as len > PAGE_SIZE) to the underlying block device,
> > causing FS corruption.
> > 
> > iomap is a generic infrastructure and it should not make any assumptions
> > about the fs block size and the page size of the system.
> 
> So what happened to the plan to making huge_zero_page a folio and have

There's a series of commits in linux-mm with the titles:

      sparc: use is_huge_zero_pmd()
      mm: add is_huge_zero_folio()
      mm: add pmd_folio()
      mm: convert migrate_vma_collect_pmd to use a folio
      mm: convert huge_zero_page to huge_zero_folio
      mm: convert do_huge_pmd_anonymous_page to huge_zero_folio
      dax: use huge_zero_folio
      mm: rename mm_put_huge_zero_page to mm_put_huge_zero_folio

> it available for non-hugetlb setups?  Not only would this be cleaner
> and more efficient, but it would actually work for the case where you'd
> have to zero more than 1MB on a 4k PAGE_SIZE system, which doesn't
> seem impossible with 2MB folios.

It is available for non-hugetlb setups.  It is however allocated on
demand, so it might not be available.