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Date:   Thu, 23 Dec 2021 09:47:09 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 48/48] mm: Use multi-index entries in the page cache
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 <20211208042256.1923824-49-willy@infradead.org>
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On Wed, Dec 08, 2021 at 04:22:56AM +0000, Matthew Wilcox (Oracle) wrote:
> We currently store large folios as 2^N consecutive entries.  While this
> consumes rather more memory than necessary, it also turns out to be buggy.
> A writeback operation which starts within a tail page of a dirty folio will
> not write back the folio as the xarray's dirty bit is only set on the
> head index.  With multi-index entries, the dirty bit will be found no
> matter where in the folio the operation starts.
> 
> This does end up simplifying the page cache slightly, although not as
> much as I had hoped.

This looks sensible to me, but I'm not xarray expert.

So the only thing I have to offer is a superficial nit:

> +static inline
> +bool folio_more_pages(struct folio *folio, pgoff_t index, pgoff_t max)

Weird identation indentation here.