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

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Date: Wed, 1 May 2024 05:13:59 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: Zi Yan <ziy@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Sean Christopherson <seanjc@...gle.com>,
	"Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
	djwong@...nel.org, brauner@...nel.org, david@...morbit.com,
	chandan.babu@...cle.com, linux-fsdevel@...r.kernel.org,
	hare@...e.de, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-xfs@...r.kernel.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 Tue, Apr 30, 2024 at 12:27:04PM -0700, Luis Chamberlain wrote:
>   2a:*	8b 43 34             	mov    0x34(%rbx),%eax		<-- trapping instruction
> RBX: 0000000000000002 RCX: 0000000000018000

Thanks, got it.  I'll send a patch in the morning, but I know exactly
what the problem is.  You're seeing sibling entries tagged as dirty.
That shouldn't happen; we should only see folios tagged as dirty.
The bug is in node_set_marks() which calls node_mark_all().  This works
fine when splitting to order 0, but we should only mark the first entry
of each order.  eg if we split to order 3, we should tag slots 0, 8,
16, 24, .., 56.