Re: [PATCH v2 00/11] fuse: optimize scatter-gather direct IO

[Maxim V. Patlasov]

Hi Miklos,

09/19/2012 08:31 PM, Maxim Patlasov ÐÐÑÐÑ:
> Hi,
>
> Existing fuse implementation processes scatter-gather direct IO in suboptimal
> way: fuse_direct_IO passes iovec[] to fuse_loop_dio and the latter calls
> fuse_direct_read/write for each iovec from iovec[] array. Thus we have as many
> submitted fuse-requests as the number of elements in iovec[] array. This is
> pure waste of resources and affects performance negatively especially for the
> case of many small chunks (e.g. page-size) packed in one iovec[] array.
>
> The patch-set amends situation in a natural way: let's simply pack as
> many iovec[] segments to every fuse-request as possible.
>
> To estimate performance improvement I used slightly modified fusexmp over
> tmpfs (clearing O_DIRECT bit from fi->flags in xmp_open). The test opened
> a file with O_DIRECT, then called readv/writev in a loop. An iovec[] for
> readv/writev consisted of 32 segments of 4K each. The throughput on some
> commodity (rather feeble) server was (in MB/sec):
>
>          original / patched
> writev: ~107     / ~480
> readv:  ~114     / ~569
>
> We're exploring possibility to use fuse for our own distributed storage
> implementation and big iovec[] arrays of many page-size chunks is typical
> use-case for device virtualization thread performing i/o on behalf of
> virtual-machine it serves.
>
> Changed in v2:
>   - inline array of page pointers req->pages[] is replaced with dynamically
>     allocated one; the number of elements is calculated a bit more
>     intelligently than being equal to FUSE_MAX_PAGES_PER_REQ; this is done
>     for the sake of memory economy.
>   - a dynamically allocated array of so-called 'page descriptors' - an offset
>     in page plus the length of fragment - is added to fuse_req; this is done
>     to simplify processing fuse requests covering several iov-s.
>
> Thanks,
> Maxim
>
> ---
>
> Maxim Patlasov (11):
>        fuse: general infrastructure for pages[] of variable size
>        fuse: categorize fuse_get_req()
>        fuse: rework fuse_retrieve()
>        fuse: rework fuse_readpages()
>        fuse: rework fuse_perform_write()
>        fuse: rework fuse_do_ioctl()
>        fuse: add per-page descriptor <offset, length> to fuse_req
>        fuse: use req->page_descs[] for argpages cases
>        fuse: pass iov[] to fuse_get_user_pages()
>        fuse: optimize fuse_get_user_pages()
>        fuse: optimize __fuse_direct_io()
>
>
>   fs/fuse/cuse.c   |    3 -
>   fs/fuse/dev.c    |   96 ++++++++++++++-------
>   fs/fuse/dir.c    |   39 ++++----
>   fs/fuse/file.c   |  250 ++++++++++++++++++++++++++++++++++++------------------
>   fs/fuse/fuse_i.h |   47 ++++++++--
>   fs/fuse/inode.c  |    6 +
>   6 files changed, 296 insertions(+), 145 deletions(-)

Any feedback on this patch-set (v2) would be highly appreciated.

Thanks,
Maxim
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