linux-kernel - Re: [PATCH 08/17] mm/filemap: add read support for RWF

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Message-ID: <66q2ojkbzy2l7ozzc4ilputbgvdtwav4r4qdvnl7x32tuutums@zachqbvl7y3w>
Date: Fri, 15 Nov 2024 10:49:08 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org, 
	clm@...a.com, linux-kernel@...r.kernel.org, willy@...radead.org, 
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, 
	bfoster@...hat.com
Subject: Re: [PATCH 08/17] mm/filemap: add read support for RWF_UNCACHED

On Thu, Nov 14, 2024 at 08:25:12AM -0700, Jens Axboe wrote:
> @@ -2595,6 +2601,20 @@ static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
>  	return (pos1 >> shift == pos2 >> shift);
>  }
>  
> +static void filemap_uncached_read(struct address_space *mapping,
> +				  struct folio *folio)
> +{
> +	if (!folio_test_uncached(folio))
> +		return;
> +	if (folio_test_writeback(folio))
> +		return;

Do we want to drop out here if the folio is dirty, but not yet under
writeback?

It is checked inside folio_unmap_invalidate(), but we will lose
PG_uncached if we get there.

> +	if (folio_test_clear_uncached(folio)) {
> +		folio_lock(folio);
> +		folio_unmap_invalidate(mapping, folio, 0);
> +		folio_unlock(folio);
> +	}
> +}
> +
>  /**
>   * filemap_read - Read data from the page cache.
>   * @iocb: The iocb to read.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov