Re: [RFC v3 0/4] vfs: Non-blockling buffered fs read (page cache only)

On Thu 25-09-14 06:06:14, Michael Kerrisk wrote:

Hello Milosz,

On Wed, Sep 24, 2014 at 11:46 PM, Milosz Tanski [off-list ref] wrote:

quoted

This patcheset introduces an ability to perform a non-blocking read from
regular files in buffered IO mode. This works by only for those filesystems
that have data in the page cache.

It does this by introducing new syscalls new syscalls preadv2/pwritev2. These
new syscalls behave like the network sendmsg, recvmsg syscalls that accept an
extra flag argument (RWF_NONBLOCK).

It's a very common patern today (samba, libuv, etc..) use a large threadpool to
perform buffered IO operations. They submit the work form another thread
that performs network IO and epoll or other threads that perform CPU work. This
leads to increased latency for processing, esp. in the case of data that's
already cached in the page cache.

With the new interface the applications will now be able to fetch the data in
their network / cpu bound thread(s) and only defer to a threadpool if it's not
there. In our own application (VLDB) we've observed a decrease in latency for
"fast" request by avoiding unnecessary queuing and having to swap out current
tasks in IO bound work threads.

Since this is a change to the user-space API, could you CC future
versions of this patch set to linux-api@vgerr.kernel.org please, as

  There's typo in the address. It should be:
linux-api@vger.kernel.org

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR

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