On Tue, 03 Apr 2007 15:47:05 +1000 Rusty Russell <[EMAIL PROTECTED]> wrote:
> On Mon, 2007-04-02 at 21:57 -0700, Andrew Morton wrote: > > On Tue, 03 Apr 2007 14:45:02 +1000 Rusty Russell <[EMAIL PROTECTED]> wrote: > > > Does that mean the to function correctly every user needs some internal > > > cursor so it doesn't end up scanning the first N entries over and over? > > > > > > > If it wants to be well-behaved, and to behave as the VM expects, yes. > > > > There's an expectation that the callback will be performing some scan-based > > aging operation and of course to do LRU (or whatever) aging, the callback > > will need to remember where it was up to last time it was called. > > > > But it's just a guideline - callbacks could do something different but > > in-the-spirit, I guess. > > Hmm, actually the callers I looked at (nfs, dcache, mbcache) seem to use > an LRU list and just walk the first "nr_to_scan" entries, and nr_to_scan > is always 128. That's just because of the batching logic up in shrink_slab(). And iirc we only break the scanning into lumps of 128 items so we can add a cond_resched() into it. > Someone who keeps a cursor will be disadvantaged: the other shrinkers > could well get less effective on repeated calls, but we won't. Someone > who picks entries at random might have the same issue. To examine the balancing one would need to examine the value of total_scan in shrink_slab(), rather than looking at the value which shrink_slab() passes into the callback. > I think it is clearest to describe how we expect everyone to work, and > let whoever is getting creative worry about it themselves. > > How's this: > == > Cleanup and kernelify shrinker registration. hm, well, six-of-one, VI of the other. We save maybe four kmallocs across the entire uptime at the cost of exposing stuff kernel-side which doesn't need to be exposed. But I think we need to weed that crappiness out of XFS first. - 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/
