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Date: Mon, 1 Feb 2010 11:45:44 +0100 From: Andi Kleen <andi@...stfloor.org> To: Nick Piggin <npiggin@...e.de> Cc: Andi Kleen <andi@...stfloor.org>, Al Viro <viro@...IV.linux.org.uk>, Christoph Lameter <cl@...ux-foundation.org>, Dave Chinner <david@...morbit.com>, Alexander Viro <viro@....linux.org.uk>, Christoph Hellwig <hch@...radead.org>, Christoph Lameter <clameter@....com>, Rik van Riel <riel@...hat.com>, Pekka Enberg <penberg@...helsinki.fi>, akpm@...ux-foundation.org, Miklos Szeredi <miklos@...redi.hu>, Nick Piggin <nickpiggin@...oo.com.au>, Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org Subject: Re: dentries: dentry defragmentation On Mon, Feb 01, 2010 at 09:35:26PM +1100, Nick Piggin wrote: > > > > > I always preferred to do defrag in the opposite way. Ie. query the > > > > > slab allocator from existing shrinkers rather than opposite way > > > > > around. This lets you reuse more of the locking and refcounting etc. > > > > > > > > I looked at this for hwpoison soft offline. > > > > > > > > But it works really badly because the LRU list ordering > > > > has nothing to do with the actual ordering inside the slab pages. > > > > > > No, you don't *have* to follow LRU order. The most important thing > > > > What list would you follow then? > > You can follow the slab, as I said in the first mail. That's pretty much what Christoph's patchkit is about (with yes some details improved) > > > There's LRU, there's hast (which is as random) and there's slab > > itself. The only one who is guaranteed to match the physical > > layout in memory is slab. That is what this patchkit is trying > > to attempt. > > > > > is if you followed what I wrote is to get a pin on the objects and > > > > Which objects? You first need to collect all that belong to a page. > > How else would you do that? > > Objects that you're interested in reclaiming, I guess. I don't > understand the question. Objects that are in the same page There are really two different cases here: - Run out of memory: in this case i just want to find all the objects of any page, ideally of not that recently used pages. - I am very fragmented and want a specific page freed to get a 2MB region back or for hwpoison: same, but do it for a specific page. > Right, but as you can see it is complex to do it this way. And I > think for reclaim driven targetted reclaim, then it needn't be so > inefficient because you aren't restricted to just one page, but > in any page which is heavily fragmented (and by definition there > should be a lot of them in the system). Assuming you can identify them quickly. > > Hwpoison I don't think adds much weight, frankly. Just panic and > reboot if you get unrecoverable error. We have everything to handle This is for soft hwpoison :- offlining pages that might go bad in the future. But soft hwpoison isn't the only user. The other big one would be for large pages or other large page allocations. -Andi -- ak@...ux.intel.com -- Speaking for myself only. -- 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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