Messages in this thread | | | Date | Tue, 28 Feb 2006 23:30:51 +0100 | From | Pavel Machek <> | Subject | Re: [Patch 3/3] prepopulate/cache cleared pages |
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On Čt 23-02-06 13:41:53, Ingo Molnar wrote: > > * Andi Kleen <ak@suse.de> wrote: > > > On Thursday 23 February 2006 10:29, Arjan van de Ven wrote: > > > This patch adds an entry for a cleared page to the task struct. The main > > > purpose of this patch is to be able to pre-allocate and clear a page in a > > > pagefault scenario before taking any locks (esp mmap_sem), > > > opportunistically. Allocating+clearing a page is an very expensive > > > operation that currently increases lock hold times quite bit (in a threaded > > > environment that allocates/use/frees memory on a regular basis, this leads > > > to contention). > > > > > > This is probably the most controversial patch of the 3, since there is > > > a potential to take up 1 page per thread in this cache. In practice it's > > > not as bad as it sounds (a large degree of the pagefaults are anonymous > > > and thus immediately use up the page). One could argue "let the VM reap > > > these" but that has a few downsides; it increases locking needs but more, > > > clearing a page is relatively expensive, if the VM reaps the page again > > > in case it wasn't needed, the work was just wasted. > > > > Looks like an incredible bad hack. What workload was that again where > > it helps? And how much? I think before we can consider adding that > > ugly code you would a far better rationale. > > yes, the patch is controversial technologically, and Arjan pointed it > out above. This is nothing new - and Arjan probably submitted this to > lkml so that he can get contructive feedback.
Actually, I think I have to back Andi here. This looked like patch for inclusion (signed-off, cc-ed Andrew). And yes, Arjan pointed out that it is controversial, but the way patch was worded I could imagine Andrew merging it... Pavel -- Web maintainer for suspend.sf.net (www.sf.net/projects/suspend) wanted... - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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