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	Fri, 15 Nov 2024 20:42:49 +0000
Date: Fri, 15 Nov 2024 20:42:48 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>, Al Viro <viro@kernel.org>,
	lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
	linux-mm <linux-mm@kvack.org>, Daniel Gomez <da.gomez@samsung.com>,
	Pankaj Raghav <p.raghav@samsung.com>, Jens Axboe <axboe@kernel.dk>,
	Dave Chinner <david@fromorbit.com>, Christoph Hellwig <hch@lst.de>,
	Chris Mason <clm@fb.com>, Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO
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On Fri, Nov 15, 2024 at 11:43:10AM -0800, Linus Torvalds wrote:
> And I did find that the "do small reads entirely under RCU" didn't
> test for one condition that filemap_get_read_batch() checked for: the
> xa_is_sibling() check.

I don't think you need it:

xas_load:
                entry = xas_descend(xas, node);

xas_descend:
        while (xa_is_sibling(entry)) {
                entry = xa_entry(xas->xa, node, offset);

so I don't think xa_is_sibling() can ever be true here.

xas_next() can return a sibling entry, so it does need the extra check.