Messages in this thread | | | Subject | Re: fadvise DONTNEED implementation (or lack thereof) | From | Peter Zijlstra <> | Date | Mon, 15 Nov 2010 09:47:05 +0100 |
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On Mon, 2010-11-15 at 15:07 +0900, Minchan Kim wrote: > On Sun, Nov 14, 2010 at 2:09 PM, KOSAKI Motohiro > <kosaki.motohiro@jp.fujitsu.com> wrote: > >> On Tue, 9 Nov 2010 16:28:02 +0900 (JST), KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote: > >> > So, I don't think application developers will use fadvise() aggressively > >> > because we don't have a cross platform agreement of a fadvice behavior. > >> > > >> I strongly disagree. For a long time I have been trying to resolve > >> interactivity issues caused by my rsync-based backup script. Many kernel > >> developers have said that there is nothing the kernel can do without > >> more information from user-space (e.g. cgroups, madvise). While cgroups > >> help, the fix is round-about at best and requires configuration where > >> really none should be necessary. The easiest solution for everyone > >> involved would be for rsync to use FADV_DONTNEED. The behavior doesn't > >> need to be perfectly consistent between platforms for the flag to be > >> useful so long as each implementation does something sane to help > >> use-once access patterns. > >> > >> People seem to mention frequently that there are no users of > >> FADV_DONTNEED and therefore we don't need to implement it. It seems like > >> this is ignoring an obvious catch-22. Currently rsync has no fadvise > >> support at all, since using[1] the implemented hints to get the desired > >> effect is far too complicated^M^M^M^Mhacky to be considered > >> merge-worthy. Considering the number of Google hits returned for > >> fadvise, I wouldn't be surprised if there were countless other projects > >> with this same difficulty. We want to be able to tell the kernel about > >> our useage patterns, but the kernel won't listen. > > > > Because we have an alternative solution already. please try memcgroup :)
Using memcgroup for this is utter crap, it just contains the trainwreck, it doesn't solve it in any way.
> I think memcg could be a solution of them but fundamental solution is > that we have to cure it in VM itself. > I feel it's absolutely absurd to enable and use memcg for amending it.
Agreed..
> I wonder what's the problem in Peter's patch 'drop behind'. > http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg179576.html > > Could anyone tell me why it can't accept upstream?
Read the thread, its quite clear nobody got convinced it was a good idea and wanted to fix the use-once policy, then Rik rewrote all of page-reclaim.
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