From: John Hubbard <jhubbard@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com,
linux-mm@kvack.org, ocfs2-devel@oss.oracle.com,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH v6 01/19] mm: Return void from various readahead functions
Date: Tue, 18 Feb 2020 13:52:48 -0800 [thread overview]
Message-ID: <df31e4a4-fe1a-5826-c8e1-c66e5197e071@nvidia.com> (raw)
In-Reply-To: <20200218212115.GG24185@bombadil.infradead.org>
On 2/18/20 1:21 PM, Matthew Wilcox wrote:
> On Tue, Feb 18, 2020 at 01:05:29PM -0800, John Hubbard wrote:
>> This is an easy review and obviously correct, so:
>>
>> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
>
> Thanks
>
>> Thoughts for the future of the API:
>>
>> I will add that I could envision another patchset that went in the
>> opposite direction, and attempted to preserve the information about
>> how many pages were successfully read ahead. And that would be nice
>> to have (at least IMHO), even all the way out to the syscall level,
>> especially for the readahead syscall.
>
> Right, and that was where I went initially. It turns out to be a
> non-trivial aount of work to do the book-keeping to find out how many
> pages were _attempted_, and since we don't wait for the I/O to complete,
> we don't know how many _succeeded_, and we also don't know how many
> weren't attempted because they were already there, and how many weren't
> attempted because somebody else has raced with us and is going to attempt
> them themselves, and how many weren't attempted because we just ran out
> of memory, and decided to give up.
>
> Also, we don't know how many pages were successfully read, and then the
> system decided to evict before the program found out how many were read,
> let alone before it did any action based on that.
>
That is even worse than I initially thought. :)
> So, given all that complexity, and the fact that nobody actually does
> anything with the limited and incorrect information we tried to provide
> today, I think it's fair to say that anybody who wants to start to do
> anything with that information can delve into all the complexity around
> "what number should we return, and what does it really mean". In the
Yes, and now that you mention it, it's really tough to pick a single number
that answers the right questions that the user space caller might have. whew.
> meantime, let's just ditch the complexity and pretense that this number
> means anything.
>
Definitely. Thanks for the notes here.
thanks,
--
John Hubbard
NVIDIA
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next prev parent reply other threads:[~2020-02-18 21:53 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-17 18:45 [f2fs-dev] [PATCH v6 00/19] Change readahead API Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 01/19] mm: Return void from various readahead functions Matthew Wilcox
2020-02-18 4:47 ` Dave Chinner
2020-02-18 21:05 ` John Hubbard
2020-02-18 21:21 ` Matthew Wilcox
2020-02-18 21:52 ` John Hubbard [this message]
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 02/19] mm: Ignore return value of ->readpages Matthew Wilcox
2020-02-18 4:48 ` Dave Chinner
2020-02-18 21:33 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 03/19] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-02-18 5:03 ` Dave Chinner
2020-02-18 13:56 ` Matthew Wilcox
2020-02-18 22:46 ` Dave Chinner
2020-02-18 22:52 ` Matthew Wilcox
2020-02-18 22:22 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 04/19] mm: Rearrange readahead loop Matthew Wilcox
2020-02-18 5:08 ` Dave Chinner
2020-02-18 13:57 ` Matthew Wilcox
2020-02-18 22:48 ` Dave Chinner
2020-02-18 22:33 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 04/16] mm: Tweak readahead loop slightly Matthew Wilcox
2020-02-18 22:57 ` John Hubbard
2020-02-18 23:00 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 05/16] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 05/19] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-02-18 5:14 ` Dave Chinner
2020-02-18 23:08 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 06/16] mm: Add readahead address space operation Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 06/19] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-02-18 5:33 ` Dave Chinner
2020-02-18 23:11 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 07/16] mm: Add page_cache_readahead_limit Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 07/19] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-18 6:14 ` Dave Chinner
2020-02-18 15:42 ` Matthew Wilcox
2020-02-19 0:59 ` Dave Chinner
2020-02-19 0:01 ` John Hubbard
2020-02-19 1:02 ` Matthew Wilcox
2020-02-19 1:13 ` John Hubbard
2020-02-19 3:24 ` John Hubbard
2020-02-19 14:41 ` Matthew Wilcox
2020-02-19 14:52 ` Christoph Hellwig
2020-02-19 15:01 ` Matthew Wilcox
2020-02-19 20:24 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 08/16] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 08/19] mm: Add readahead address space operation Matthew Wilcox
2020-02-18 6:21 ` Dave Chinner
2020-02-18 16:10 ` Matthew Wilcox
2020-02-19 1:04 ` Dave Chinner
2020-02-19 0:12 ` John Hubbard
2020-02-19 3:10 ` Eric Biggers
2020-02-19 3:35 ` Eric Biggers
2020-02-19 16:52 ` Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 09/16] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 09/19] mm: Add page_cache_readahead_limit Matthew Wilcox
2020-02-18 6:31 ` Dave Chinner
2020-02-18 19:54 ` Matthew Wilcox
2020-02-19 1:08 ` Dave Chinner
2020-02-19 1:32 ` John Hubbard
2020-02-19 2:23 ` Matthew Wilcox
2020-02-19 2:46 ` John Hubbard
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 10/16] erofs: Convert uncompressed files from readpages to readahead Matthew Wilcox
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 10/19] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-18 1:51 ` [f2fs-dev] [Ocfs2-devel] " Joseph Qi
2020-02-18 6:37 ` [f2fs-dev] " Dave Chinner
2020-02-19 2:48 ` John Hubbard
2020-02-19 3:28 ` Eric Biggers
2020-02-19 3:47 ` Matthew Wilcox
2020-02-19 3:55 ` Eric Biggers
2020-02-17 18:45 ` [f2fs-dev] [PATCH v6 11/19] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-18 6:57 ` Dave Chinner
2020-02-18 21:12 ` Matthew Wilcox
2020-02-19 1:23 ` Dave Chinner
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 11/16] erofs: Convert compressed files " Matthew Wilcox
2020-02-19 2:34 ` Gao Xiang
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 12/19] erofs: Convert uncompressed " Matthew Wilcox
2020-02-19 2:39 ` Gao Xiang
2020-02-19 3:04 ` Dave Chinner
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 12/16] ext4: Convert " Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 13/19] erofs: Convert compressed files " Matthew Wilcox
2020-02-19 3:08 ` Dave Chinner
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 13/16] f2fs: Convert " Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 14/19] ext4: " Matthew Wilcox
2020-02-19 3:16 ` Dave Chinner
2020-02-19 3:29 ` Eric Biggers
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 14/16] fuse: " Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 15/19] f2fs: " Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 15/16] iomap: " Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 16/19] fuse: " Matthew Wilcox
2020-02-19 3:22 ` Dave Chinner
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 16/16] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 17/19] iomap: Restructure iomap_readpages_actor Matthew Wilcox
2020-02-19 3:17 ` John Hubbard
2020-02-19 5:35 ` Matthew Wilcox
2020-02-19 3:29 ` Dave Chinner
2020-02-19 6:04 ` Matthew Wilcox
2020-02-19 6:40 ` Dave Chinner
2020-02-19 17:06 ` Matthew Wilcox
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 18/19] iomap: Convert from readpages to readahead Matthew Wilcox
2020-02-19 3:40 ` Dave Chinner
2020-02-17 18:46 ` [f2fs-dev] [PATCH v6 19/19] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-02-19 3:43 ` Dave Chinner
2020-02-19 5:22 ` Matthew Wilcox
2020-02-17 18:48 ` [f2fs-dev] [PATCH v6 00/19] Change readahead API Matthew Wilcox
2020-02-18 4:56 ` Dave Chinner
2020-02-18 13:42 ` Matthew Wilcox
2020-02-18 21:26 ` Dave Chinner
2020-02-19 3:45 ` Dave Chinner
2020-02-19 3:48 ` Matthew Wilcox
2020-02-19 3:57 ` Dave Chinner
2020-02-18 20:49 ` John Hubbard
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