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From: Christoph Hellwig <hch@infradead.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org
Subject: Re: [PATCHSET 0/5] Support for RWF_UNCACHED
Date: Thu, 12 Dec 2019 07:47:52 -0800	[thread overview]
Message-ID: <20191212154752.GA3936@infradead.org> (raw)
In-Reply-To: <20191210162454.8608-1-axboe@kernel.dk>

On Tue, Dec 10, 2019 at 09:24:49AM -0700, Jens Axboe wrote:
> Seems to me that we have an opportunity to provide something that sits
> somewhere in between buffered and O_DIRECT, and this is where
> RWF_UNCACHED enters the picture. If this flag is set on IO, we get the
> following behavior:
> 
> - If the data is in cache, it remains in cache and the copy (in or out)
>   is served to/from that.
> 
> - If the data is NOT in cache, we add it while performing the IO. When
>   the IO is done, we remove it again.
> 
> With this, I can do 100% smooth buffered reads or writes without pushing
> the kernel to the state where kswapd is sweating bullets. In fact it
> doesn't even register.
> 
> Comments appreciated! Patches are against current git (ish), and can
> also be found here:

I can't say I particularly like the model, as it still has all the
page cache overhead.  Direct I/O with bounce buffers for unaligned I/O
sounds simpler and faster to me.

  parent reply	other threads:[~2019-12-12 15:47 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-10 16:24 [PATCHSET 0/5] Support for RWF_UNCACHED Jens Axboe
2019-12-10 16:24 ` [PATCH 1/5] fs: add read support " Jens Axboe
2019-12-10 16:24 ` [PATCH 2/5] mm: make generic_perform_write() take a struct kiocb Jens Axboe
2019-12-10 16:24 ` [PATCH 3/5] mm: make buffered writes work with RWF_UNCACHED Jens Axboe
2019-12-10 16:55   ` Matthew Wilcox
2019-12-10 17:02     ` Jens Axboe
2019-12-10 18:35       ` Chris Mason
2019-12-10 18:58       ` Matthew Wilcox
2019-12-10 19:10         ` Jens Axboe
2019-12-11  0:23   ` Dave Chinner
2019-12-11  0:28     ` Dave Chinner
2019-12-11 14:39     ` Jens Axboe
2019-12-10 16:24 ` [PATCH 4/5] iomap: pass in the write_begin/write_end flags to iomap_actor Jens Axboe
2019-12-10 16:24 ` [PATCH 5/5] iomap: support RWF_UNCACHED for buffered writes Jens Axboe
2019-12-10 21:17 ` [PATCHSET 0/5] Support for RWF_UNCACHED Andreas Dilger
2019-12-12 15:47 ` Christoph Hellwig [this message]
2019-12-12 15:52   ` Jens Axboe

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