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2020 Aug 07
3
[PATCH nbdkit] file: Implement cache=none and fadvise=normal|random|sequential.
You can use these flags as described in the manual page to optimize
access patterns, and to get better behaviour with the page cache in
some scenarios.
For my testing I used the cachedel and cachestats utilities written by
Julius Plenz (https://github.com/Feh/nocache). I started with a 32 GB
file of random data on a machine with about 32 GB of RAM. At the
beginning of the test I evicted the file from the page cache:
$ cachedel /var/tmp/random
$ cachestats /var/tmp/random
pages in cache: 0/838...
2020 Aug 07
0
Re: [PATCH nbdkit] file: Implement cache=none and fadvise=normal|random|sequential.
...; You can use these flags as described in the manual page to optimize
> access patterns, and to get better behaviour with the page cache in
> some scenarios.
And if you guess wrong, it is only a performance penalty, not a
correctness issue.
>
> For my testing I used the cachedel and cachestats utilities written by
> Julius Plenz (https://github.com/Feh/nocache). I started with a 32 GB
> file of random data on a machine with about 32 GB of RAM. At the
> beginning of the test I evicted the file from the page cache:
>
> $ cachedel /var/tmp/random
> $ cachestats /var/tm...
2020 Aug 07
3
Re: [PATCH nbdkit] file: Implement cache=none and fadvise=normal|random|sequential.
...20 at 07:53:13AM -0500, Eric Blake wrote:
> >$ free -m; time ./nbdkit file /var/tmp/random fadvise=sequential cache=none --run 'qemu-img convert -n -p -m 16 -W $nbd "json:{\"file.driver\":\"null-co\",\"file.size\":\"1E\"}"' ; free -m ; cachestats /var/tmp/random
>
> Hmm - the -W actually says that qemu-img is performing semi-random
> access (there is no guarantee that the 16 coroutines are serviced in
> linear order of the file), even though we really are making only one
> pass through the file in bulk. I don't know if...
2020 Aug 07
0
Re: [PATCH nbdkit] file: Implement cache=none and fadvise=normal|random|sequential.
...00, Eric Blake wrote:
> > >$ free -m; time ./nbdkit file /var/tmp/random fadvise=sequential
> cache=none --run 'qemu-img convert -n -p -m 16 -W $nbd
> "json:{\"file.driver\":\"null-co\",\"file.size\":\"1E\"}"' ; free -m ;
> cachestats /var/tmp/random
> >
> > Hmm - the -W actually says that qemu-img is performing semi-random
> > access (there is no guarantee that the 16 coroutines are serviced in
> > linear order of the file), even though we really are making only one
> > pass through the file in bu...