On Wed, 2007-03-07 at 14:08 +0100, Nick Piggin wrote: > > > The thing is, I don't think anybody who uses these things cares > > > about any of the 'problems' you want to fix, do they? We are > > > interested in dirty pages only for the correctness issue, rather > > > than performance. Same as reclaim. > > > > If so, we can just stick to the dead slow but correct 'scan the full > > vma' page_mkclean() and nobody would ever trigger it. > > Not if we restricted it to root and mlocked tmpfs. But then why > wouldn't you just do it with the much more efficient msync walk, > so that if root does want to do writeout via these things, it does > not blow up?
This is all used on ram based filesystems right, they all have BDI_CAP_NO_WRITEBACK afaik, so page_mkclean will never get called anyway. Mlock doesn't avoid getting page_mkclean called. Those who use this on a 'real' filesystem will get hit in the face by a linear scanning page_mkclean(), but AFAIK nobody does this anyway. Restricting it to root for such filesystems is unwanted, that'd severely handicap both UML and Oracle as I understand it (are there other users of this feature around?) msync() might never get called and then we're back with the old behaviour where we can surprise the VM with a ton of dirty pages. > > What is the DoS scenario wrt reclaim? We really ought to fix that if > > real, those UML farms run on nothing but nonlinear reclaim I'd think. > > I guess you can just increase the computational complexity of > reclaim quite easily. Right, on first glance it doesn't look to be too bad, but I should take a closer look. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
