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From: John Hubbard <jhubbard@nvidia.com>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	<linux-fsdevel@vger.kernel.org>, <linux-mm@kvack.org>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 18/25] btrfs: Use readahead_batch_length
Date: Thu, 17 Dec 2020 01:15:10 -0800	[thread overview]
Message-ID: <a5b979d7-1086-fe6c-6e82-f20ecb56d24c@nvidia.com> (raw)
In-Reply-To: <20201216182335.27227-19-willy@infradead.org>

On 12/16/20 10:23 AM, Matthew Wilcox (Oracle) wrote:
> Implement readahead_batch_length() to determine the number of bytes in
> the current batch of readahead pages and use it in btrfs.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>   fs/btrfs/extent_io.c    | 6 ++----
>   include/linux/pagemap.h | 9 +++++++++
>   2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 6e3b72e63e42..42936a83a91b 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4436,10 +4436,8 @@ void extent_readahead(struct readahead_control *rac)
>   	int nr;
>   
>   	while ((nr = readahead_page_batch(rac, pagepool))) {
> -		u64 contig_start = page_offset(pagepool[0]);
> -		u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1;
> -
> -		ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end);
> +		u64 contig_start = readahead_pos(rac);
> +		u64 contig_end = contig_start + readahead_batch_length(rac);

Something in this tiny change is breaking btrfs: it hangs my Fedora 33 test
system (which changed over to btrfs) on boot. I haven't quite figured out
what's really wrong, but git bisect lands here, *and* turning the whole
extent_readahead() function into a no-op (on top of the whole series)
allows everything to work once again.

Sorry for not actually solving the root cause, but I figured you'd be able
to jump straight to the answer, with the above information, so I'm sending
it out early.


thanks,
-- 
John Hubbard
NVIDIA

  reply	other threads:[~2020-12-17  9:16 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-16 18:23 [PATCH 00/25] Page folios Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 01/25] mm: Introduce struct folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 02/25] mm: Add put_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 03/25] mm: Add get_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 04/25] mm: Create FolioFlags Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 05/25] mm: Add unlock_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 06/25] mm: Add lock_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 07/25] mm: Add lock_folio_killable Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 08/25] mm: Add __alloc_folio_node and alloc_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 09/25] mm: Convert __page_cache_alloc to return a folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 10/25] mm/filemap: Convert end_page_writeback to use " Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 11/25] mm: Convert mapping_get_entry to return " Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 12/25] mm: Add mark_folio_accessed Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 13/25] mm: Add filemap_get_folio and find_get_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 14/25] mm/filemap: Add folio_add_to_page_cache Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 15/25] mm/swap: Convert rotate_reclaimable_page to folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 16/25] mm: Add folio_mapping Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 17/25] mm: Rename THP_SUPPORT to MULTI_PAGE_FOLIOS Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 18/25] btrfs: Use readahead_batch_length Matthew Wilcox (Oracle)
2020-12-17  9:15   ` John Hubbard [this message]
2020-12-17 12:12     ` Matthew Wilcox
2020-12-17 13:42       ` Matthew Wilcox
2020-12-17 19:36         ` John Hubbard
2020-12-16 18:23 ` [PATCH 19/25] fs: Change page refcount rules for readahead Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 20/25] fs: Change readpage to take a folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 21/25] mm: Convert wait_on_page_bit to wait_on_folio_bit Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 22/25] mm: Add wait_on_folio_locked & wait_on_folio_locked_killable Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 23/25] mm: Add flush_dcache_folio Matthew Wilcox (Oracle)
2020-12-16 20:59   ` kernel test robot
2020-12-16 20:59     ` kernel test robot
2020-12-16 22:01     ` Matthew Wilcox
2020-12-16 22:01       ` Matthew Wilcox
2020-12-16 18:23 ` [PATCH 24/25] mm: Add read_cache_folio and read_mapping_folio Matthew Wilcox (Oracle)
2020-12-16 18:23 ` [PATCH 25/25] fs: Convert vfs_dedupe_file_range_compare to folios Matthew Wilcox (Oracle)
2020-12-17 12:47 ` [PATCH 00/25] Page folios David Hildenbrand
2020-12-17 13:55   ` Matthew Wilcox
2020-12-17 14:35     ` David Hildenbrand

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