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    SubjectRe: Unexpected splice "always copy" behavior observed
    Sorry for deleting CC'd addresses. yahoo was whining...

    --- On Wed, 5/19/10, Linus Torvalds <torvalds@linux-foundation.org> wrote:

    > From: Linus Torvalds <torvalds@linux-foundation.org>
    > Subject: Re: Unexpected splice "always copy" behavior observed
    > To: "Steven Rostedt" <rostedt@goodmis.org>
    > Cc: "Nick Piggin" <npiggin@suse.de>, "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>, "Peter Zijlstra" <peterz@infradead.org>, "Frederic Weisbecker" <fweisbec@gmail.com>, "Pierre Tardy" <tardyp@gmail.com>, "Ingo Molnar" <mingo@elte.hu>, "Arnaldo Carvalho de Melo" <acme@redhat.com>, "Tom Zanussi" <tzanussi@gmail.com>, "Paul Mackerras" <paulus@samba.org>, linux-kernel@vger.kernel.org, arjan@infradead.org, ziga.mahkovec@gmail.com, "davem" <davem@davemloft.net>, linux-mm@kvack.org, "Andrew Morton" <akpm@linux-foundation.org>, "KOSAKI Motohiro" <kosaki.motohiro@jp.fujitsu.com>, "Christoph Lameter" <cl@linux-foundation.org>, "Tejun Heo" <tj@kernel.org>, "Jens Axboe" <jens.axboe@oracle.com>
    > Date: Wednesday, May 19, 2010, 2:59 PM
    >
    >
    > On Wed, 19 May 2010, Steven Rostedt wrote:
    >
    > > On Wed, 2010-05-19 at 07:39 -0700, Linus Torvalds
    > wrote:
    > >
    > > > The real limitation is likely always going to be
    > the fact that it has to
    > > > be page-aligned and a full page. For a lot of
    > splice inputs, that simply
    > > > won't be the case, and you'll end up copying for
    > alignment reasons anyway.
    > >
    > > That's understandable. For the use cases of splice I
    > use, I work to make
    > > it page aligned and full pages. Anyone else using
    > splice for
    > > optimizations, should do the same. It only makes
    > sense.
    > >
    > > The end of buffer may not be a full page, but then
    > it's the end anyway,
    > > and I'm not as interested in the speed.
    >
    > Btw, since you apparently have a real case - is the "splice
    > to file"
    > always just an append? IOW, if I'm not right in assuming
    > that the only
    > sane thing people would reasonable care about is "append to
    > a file", then
    > holler now.
    >

    I've a similar 'append' use case:
    http://marc.info/?l=linux-kernel&m=127143736527459&w=4

    My mmapped buffers are pinned down.






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