On Mon, 30 Jun 2014 17:48:03 +0100 Mel Gorman <mgorman@xxxxxxx> wrote: > The fair zone allocation policy round-robins allocations between zones > within a node to avoid age inversion problems during reclaim. If the > first allocation fails, the batch counts is reset and a second attempt > made before entering the slow path. > > One assumption made with this scheme is that batches expire at roughly the > same time and the resets each time are justified. This assumption does not > hold when zones reach their low watermark as the batches will be consumed > at uneven rates. Allocation failure due to watermark depletion result in > additional zonelist scans for the reset and another watermark check before > hitting the slowpath. > > This patch makes a number of changes that should reduce the overall cost > > o Abort the fair zone allocation policy once remote zones are encountered > o Use a simplier scan when resetting NR_ALLOC_BATCH > o Use a simple flag to identify depleted zones instead of accessing a > potentially write-intensive cache line for counters > > On UMA machines, the effect on overall performance is marginal. The main > impact is on system CPU usage which is small enough on UMA to begin with. > This comparison shows the system CPu usage between vanilla, the previous > patch and this patch. > > 3.16.0-rc2 3.16.0-rc2 3.16.0-rc2 > vanilla checklow-v4 fairzone-v4 > User 390.13 400.85 396.13 > System 404.41 393.60 389.61 > Elapsed 5412.45 5166.12 5163.49 > > There is a small reduction and it appears consistent. > > On NUMA machines, the scanning overhead is higher as zones are scanned > that are ineligible for use by zone allocation policy. This patch fixes > the zone-order zonelist policy and reduces the numbers of zones scanned > by the allocator leading to an overall reduction of CPU usage. > > 3.16.0-rc2 3.16.0-rc2 3.16.0-rc2 > vanilla checklow-v4 fairzone-v4 > User 744.05 763.26 778.53 > System 70148.60 49331.48 44905.73 > Elapsed 28094.08 27476.72 27378.98 That's a large change in system time. Does this all include kswapd activity? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
