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

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Message-ID: <Z_gotADO2ba-Qz9Z@casper.infradead.org>
Date: Thu, 10 Apr 2025 21:23:16 +0100
From: Matthew Wilcox <willy@...radead.org>
To: 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

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.

>  static inline unsigned int folio_large_order(const struct folio *folio)
>  {
> -	return folio->_flags_1 & 0xff;
> +	return FIELD_GET(FOLIO_ORDER_MASK, folio->_flags_1);
>  }
>  
>  #ifdef NR_PAGES_IN_LARGE_FOLIO