On Sat, Jun 02 2007, Linus Torvalds wrote:
>
>
> On Sat, 2 Jun 2007, Jens Axboe wrote:
> >
> > splice() WILL return EAGAIN, but in that case it should have triggered
> > the read-ahead and thus started some IO.
>
> That's not enough.
>
> If the IO has already been started, splice needs to wait.
But splice doesn't know, page_cache_readahead() may not have started
anything.
> > For the from-file case, see __generic_file_splice_read(). splice does:
> >
> > if (!PageUptodate(page)) {
> > /*
> > * If in nonblock mode then dont block on
> > * waiting
> > * for an in-flight io page
> > */
> > if (flags & SPLICE_F_NONBLOCK) {
> > if (TestSetPageLocked(page))
> > break;
> > } else
> > lock_page(page);
>
> Yeah, that's just wrong.
>
> Your suggested:
>
> > if ((flags & SPLICE_F_NONBLOCK) && spd.nr_pages) {
> > if (TestSetPageLocked(page))
> > break;
> > } else
> > lock_page(page);
> >
> > should do that - always block for the first page and potentially return
> > a partial results for the remaining pages that read-ahead kicked into
> > gear.
>
> would work, but I suspect that for a server, returning EAGAIN once is
> actually the best option - if it has a select() loop, and something else
> is running, the "return EAGAIN once" actually makes tons of sense (it
> would basically boil down to the kernel effectively saying "ok, try
> anything else you might have pending in your queues first, if you get back
> to me, I'll block then").
Well then the current code should work, _provided_ that we know
read-ahead kicked off the IO. Well almost, still needs a bit of
tweaking, with some knowledge of whether page_cache_readahead() actually
called into read_pages() or not.
--
Jens Axboe
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
