linux-kernel - Re: [PATCH v4 05/11] mm: do not split a folio if it has minimum folio order requirement

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Message-ID: <Ziq4qAJ_p7P9Smpn@casper.infradead.org>
Date: Thu, 25 Apr 2024 21:10:16 +0100
From: Matthew Wilcox <willy@...radead.org>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: 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 05/11] mm: do not split a folio if it has minimum
 folio order requirement

On Thu, Apr 25, 2024 at 01:37:40PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.com>
> 
> Splitting a larger folio with a base order is supported using
> split_huge_page_to_list_to_order() API. However, using that API for LBS
> is resulting in an NULL ptr dereference error in the writeback path [1].
> 
> Refuse to split a folio if it has minimum folio order requirement until
> we can start using split_huge_page_to_list_to_order() API. Splitting the
> folio can be added as a later optimization.
> 
> [1] https://gist.github.com/mcgrof/d12f586ec6ebe32b2472b5d634c397df

Obviously this has to be tracked down and fixed before this patchset can
be merged ... I think I have some ideas.  Let me look a bit.  How
would I go about reproducing this?