On Wed, 2012-09-12 at 12:27 -0700, Andrew Morton wrote: > > That sounds good, although more details on the performance changes > would be appreciated - after all, that's the entire point of the > patchset. > > And we shouldn't only test for improvements - we should also test for > degradation. What workloads might be harmed by this change? I'd suggest > > - a single process which opens N files and reads one page from each > one, then repeats. So there are no contiguous LRU pages which share > the same ->mapping. Get some page reclaim happening, measure the > impact. > > - The batching means that we now do multiple passes over pageframes > where we used to do things in a single pass. Walking all those new > page lists will be expensive if they are lengthy enough to cause L1 > cache evictions.
I need to address both your concerns and Mel's concerns about the downside of prolonging the holding page locks for the pages to be unmmaped for patch 1 in the series. I'll try to do some testing to see what kind of benefit I get by only batching operations under the i_mmap_mutex (i.e. patch 2 and 3 only) and not do batch unmap. Those other changes don't have the downsides of prolonged page locking and we can incorporate them with less risks. > > What would be a test for this? A simple, single-threaded walk > through a file, I guess? Thanks for your test suggestions. I will do tests along your suggestions when I generate the next iterations of the patch. I've been playing with these patches for a while and they are based on 3.4 kernel. I'll move them to 3.6 kernel in my next iteration. > > Mel's review comments were useful, thanks. Very much appreciate comments from you, Mel and Minchan. I'll try to incorporate them in my changes. Tim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
