linux-kernel - Re: [PATCH v1] fs/dax: fix folio splitting issue by resetting old folio order + _nr

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Message-ID: <67f82e0e234ea_720529471@dwillia2-xfh.jf.intel.com.notmuch>
Date: Thu, 10 Apr 2025 13:46:06 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Matthew Wilcox <willy@...radead.org>, Dan Williams
	<dan.j.williams@...el.com>
CC: David Hildenbrand <david@...hat.com>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <linux-fsdevel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, Alison Schofield <alison.schofield@...el.com>,
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner
	<brauner@...nel.org>, Jan Kara <jack@...e.cz>, Andrew Morton
	<akpm@...ux-foundation.org>, Alistair Popple <apopple@...dia.com>, "Christoph
 Hellwig" <hch@...radead.org>
Subject: Re: [PATCH v1] fs/dax: fix folio splitting issue by resetting old
 folio order + _nr_pages

Matthew Wilcox wrote:
> On Thu, Apr 10, 2025 at 01:15:07PM -0700, Dan Williams wrote:
> > For consistency and clarity what about this incremental change, to make
> > the __split_folio_to_order() path reuse folio_reset_order(), and use
> > typical bitfield helpers for manipulating _flags_1?
> 
> I dislike this intensely.  It obfuscates rather than providing clarity.

I'm used to pushing folks to use bitfield.h in driver land, but will not
push it further here.

What about this hunk?

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2a47682d1ab7..301ca9459122 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3404,7 +3404,7 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
 	if (new_order)
 		folio_set_order(folio, new_order);
 	else
-		ClearPageCompound(&folio->page);
+		folio_reset_order(folio);
 }
 
 /*