[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CALZtONDAitXFfQWPfWG2Qy03NY7Q-2Asch0xQn0FEa-A6oNZTg@mail.gmail.com>
Date: Tue, 12 Nov 2013 09:24:55 -0500
From: Dan Streetman <ddstreet@...e.org>
To: Bob Liu <bob.liu@...cle.com>
Cc: sjennings@...iantweb.net, linux-mm@...ck.org,
linux-kernel <linux-kernel@...r.kernel.org>, minchan@...nel.org,
weijie.yang@...sung.com, k.kozlowski@...sung.com,
konrad.wilk@...cle.com
Subject: Re: mm/zswap: change to writethrough
On Tue, Nov 12, 2013 at 4:11 AM, Bob Liu <bob.liu@...cle.com> wrote:
>
> On 11/12/2013 03:12 AM, Dan Streetman wrote:
>> Seth, have you (or anyone else) considered making zswap a writethrough
>> cache instead of writeback? I think that it would significantly help
>> the case where zswap fills up and starts writing back its oldest pages
>> to disc - all the decompression work would be avoided since zswap
>> could just evict old pages and forget about them, and it seems likely
>> that when zswap is full that's probably the worst time to add extra
>> work/delay, while adding extra disc IO (presumably using dma) before
>> zswap is full doesn't seem to me like it would have much impact,
>> except in the case where zswap isn't full but there is so little free
>> memory that new allocs are waiting on swap-out.
>>
>> Besides the additional disc IO that obviously comes with making zswap
>> writethrough (additional only before zswap fills up), are there any
>> other disadvantages? Is it a common situation for there to be no
>> memory left and get_free_page actively waiting on swap-out, but before
>> zswap fills up?
>>
>> Making it writethrough also could open up other possible improvements,
>> like making the compression and storage of new swap-out pages async,
>> so the compression doesn't delay the write out to disc.
>>
>
> I like this idea and those benefits, the only question I'm not sure is
> would it be too complicate to implement this feature? It sounds like we
> need to reimplement something like swapcache to handle zswap write through.
Simply converting to writethrough should be as easy as returning
non-zero from zswap_frontswap_store(), although
zswap_writeback_entry() also needs simplification to skip the
writeback. I think it shouldn't be difficult; I'll start working on a
first pass of a patch.
Thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists