Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 15 Nov 2010 18:05:00 +0900 | Subject | Re: fadvise DONTNEED implementation (or lack thereof) | From | Minchan Kim <> |
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On Mon, Nov 15, 2010 at 5:47 PM, Peter Zijlstra <peterz@infradead.org> wrote: > 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. >
Thanks for the information. I hope this is a chance to rethink about it. Rik, Could you give us to any comment about this idea?
-- Kind regards, Minchan Kim -- 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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