From: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
To: valdis.kletnieks@vt.edu
Cc: Adam Borowski <kilobyte@angband.pl>,
kernelnewbies@kernelnewbies.org,
Pintu Agarwal <pintu.ping@gmail.com>,
open list <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org
Subject: Re: Creating compressed backing_store as swapfile
Date: Mon, 5 Nov 2018 11:55:58 -0500 [thread overview]
Message-ID: <20fe7145-8426-c67d-2ab2-258ec5717966@gmail.com> (raw)
Message-ID: <20181105165558.UX2OFVgro6AiPHK2PmedUeduX_8P9PmcGXB4374vOTE@z> (raw)
In-Reply-To: <83467.1541436836@turing-police.cc.vt.edu>
On 11/5/2018 11:53 AM, valdis.kletnieks@vt.edu wrote:
> On Mon, 05 Nov 2018 11:28:49 -0500, "Austin S. Hemmelgarn" said:
>
>> Also, it's probably worth noting that BTRFS doesn't need to decompress
>> the entire file to read or write blocks in the middle, it splits the
>> file into 128k blocks and compresses each of those independent of the
>> others, so it can just decompress the 128k block that holds the actual
>> block that's needed.
>
> Presumably it does something sane with block allocation for the now-compressed
> 128K that's presumably much smaller. Also, that limits the damage from writing to
> the middle of a compression unit....
>
> That *does* however increase the memory requirement - you can OOM or
> deadlock if your read/write from the swap needs an additional 128K for the
> compression buffer at an inconvenient time...
>
Indeed, and I can't really comment on how it might behave under those
circumstances (the systems I did the testing on never saw memory
pressure quite _that_ bad, and I had them set up to swap things out
pretty early and really aggressively).
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next prev parent reply other threads:[~2018-11-05 16:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-05 15:01 Creating compressed backing_store as swapfile Pintu Agarwal
2018-11-05 15:01 ` Pintu Agarwal
[not found] ` <20181105155815.i654i5ctmfpqhggj@angband.pl>
2018-11-05 16:07 ` Austin S. Hemmelgarn
2018-11-05 16:07 ` Austin S. Hemmelgarn
2018-11-05 16:14 ` valdis.kletnieks at vt.edu
2018-11-05 16:14 ` valdis.kletnieks
2018-11-05 16:28 ` Austin S. Hemmelgarn
2018-11-05 16:28 ` Austin S. Hemmelgarn
2018-11-05 16:53 ` valdis.kletnieks at vt.edu
2018-11-05 16:53 ` valdis.kletnieks
2018-11-05 16:55 ` Austin S. Hemmelgarn [this message]
2018-11-05 16:55 ` Austin S. Hemmelgarn
2018-11-08 9:51 ` Pintu Agarwal
2018-11-08 9:51 ` Pintu Agarwal
2018-11-05 16:12 ` valdis.kletnieks at vt.edu
2018-11-05 16:12 ` valdis.kletnieks
2018-11-08 9:46 ` Pintu Agarwal
2018-11-08 9:46 ` Pintu Agarwal
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