linux-kernel - Re: [PATCH v4 07/11] iomap: fix iomap_dio

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Date: Fri, 26 Apr 2024 21:52:41 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Christoph Hellwig <hch@...radead.org>,
	"Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
	djwong@...nel.org, brauner@...nel.org, david@...morbit.com,
	chandan.babu@...cle.com, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, hare@...e.de,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-xfs@...r.kernel.org, mcgrof@...nel.org, gost.dev@...sung.com,
	p.raghav@...sung.com
Subject: Re: [PATCH v4 07/11] iomap: fix iomap_dio_zero() for fs bs > system
 page size

On Sat, Apr 27, 2024 at 04:26:44AM +0100, Matthew Wilcox wrote:
> 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.

We could just export get_huge_zero_page/put_huge_zero_page and make
sure it is is available for block sizse > PAGE_SIZE file systems, or
is there a good argument against that?