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Date: Thu, 8 May 2025 16:03:21 +0200
From: Christoph Hellwig <hch@lst.de>
To: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ryusuke Konishi <konishi.ryusuke@gmail.com>,
	Hugh Dickins <hughd@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Yosry Ahmed <yosry.ahmed@linux.dev>, Nhat Pham <nphamcs@gmail.com>,
	Chengming Zhou <chengming.zhou@linux.dev>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	linux-nilfs@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/7] mm: stop passing a writeback_control structure to
 shmem_writeout
Message-ID: <20250508140321.GA31543@lst.de>
References: <20250508054938.15894-1-hch@lst.de> <20250508054938.15894-3-hch@lst.de> <aBywrEMTCKfT9BFo@casper.infradead.org>
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On Thu, May 08, 2025 at 02:25:00PM +0100, Matthew Wilcox wrote:
> This got me to look at why we need to keep wbc in __shmem_writeback().
> We only have it because folio_redirty_for_writepage() needs it.  And
> folio_redirty_for_writepage() only needs it because it updates
> pages_skipped.

in linux-next you also changed it to use writeback_iter, which needs
the wbc as well.  That probably as an improvement compared to the
previous version, but overall it still feels odd.

> I'm not quite sure if we can simply call filemap_dirty_folio() here
> or whether mapping_can_writeback() is true for shmem and we need to
> do all the other things -- in which case we could just change that one
> line to

shmem doesn't set up a bdi, so it should not be true.