Re: [PATCH] updated reiser4 - reduced cpu usage for writes by writing more than 4k at a time (has implications for generic write code and eventually for the IO layer)

["Alexey Polyakov" <alexey.polyakov@gmail.com>]

Hi!

I'm actively using Reiser4 on a production servers (and I know a lot
of people that do that too).
Could you please release the patch against the vanilla tree?
I don't think there's a lot of people that will test -mm version,
especially on production servers - -mm is a little bit too unstable.

Thanks.


On 5/24/06, Hans Reiser <reiser@namesys.com> wrote:
> ftp://ftp.namesys.com/pub/reiser4-for-2.6/2.6.17-rc4-mm1/reiser4-for-2.6.17-rc4-mm1-2.patch.gz
>
> The referenced patch replaces all reiser4 patches to mm.  It revises the
> existing reiser4 code to do a good job for writes that are larger than
> 4k at a time by assiduously adhering to the principle that things that
> need to be done once per write should be done once per write, not once
> per 4k.  That statement is a slight simplification: there are times when
> due to the limited size of RAM you want to do some things once per
> WRITE_GRANULARITY, where WRITE_GRANULARITY is a #define that defines
> some moderate number of pages to write at once.  This code empirically
> proves that the generic code design which passes 4k at a time to the
> underlying FS can be improved.  Performance results show that the new
> code consumes  40% less CPU when doing "dd bs=1MB ....." (your hardware,
> and whether the data is in cache, may vary this result).  Note that this
> has only a small effect on elapsed time for most hardware.
>
> The planned future(as discussed with akpm previously):  we will ship
> very soon (testing it now) an improved reiser4 read code that does reads
> in more than little 4k chunks.  Then we will revise the generic code to
> allow an FS to receive the writes and reads in whole increments.  How
> best to revise the generic code is still being discussed.  Nate is
> discussing doing it in some way that improves code symmetry in the io
> scheduler layer as well, if there is interest by others in it maybe a
> thread can start on that topic, or maybe it can wait for him+zam to make
> a patch.
>
> Note for users: this patch also contains numerous important bug fixes.
>
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--
Alexey Polyakov
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