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Date: Sun, 1 Jun 2008 01:15:01 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Hugh Dickins <hugh@...itas.com> Cc: Pavel Machek <pavel@....cz>, kernel list <linux-kernel@...r.kernel.org>, "Rafael J. Wysocki" <rjw@...k.pl> Subject: Re: sync_file_range(SYNC_FILE_RANGE_WRITE) blocks? On Sun, 1 Jun 2008 08:23:43 +0100 (BST) Hugh Dickins <hugh@...itas.com> wrote: > On Sat, 31 May 2008, Andrew Morton wrote: > > On Sat, 31 May 2008 19:44:49 +0100 (BST) Hugh Dickins <hugh@...itas.com> wrote: > > > > > > All I can say so far is that I find the same as you do: > > > SYNC_FILE_RANGE_WRITE (after writing) takes a significant amount of time, > > > more than half as long as when you add in SYNC_FILE_RANGE_WAIT_AFTER too. > > > > > > Which make the sync_file_range call pretty pointless: your usage seems > > > perfectly reasonable to me, but somehow we've broken its behaviour. > > > I'll be investigating ... > > > > It will block on disk queue fullness - sysrq-W will tell. > > Ah, thank you. What a disappointment, though it's understandable. > Doesn't that very severely limit the usefulness of the system call? A bit. The request queue size is runtime tunable though. I expect major users of this system call will be applications which do small-sized overwrites into large files, mainly databases. That is, once the application developers discover its existence. I'm still getting expressions of wonder from people who I tell about the five-year-old fadvise(). > I admit the flag isn't called SYNC_FILE_RANGE_WRITE_WITHOUT_WAITING, > but I don't suppose Pavel and I are the only ones misled by it. Yup, this caveat/restriction should be in the manpage. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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