On Thu, Jun 24, 2021 at 11:18:57PM +0900, Wonhyuk Yang wrote: > On Wed, Jun 23, 2021 at 6:15 PM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Sun, Jun 20, 2021 at 11:57:42PM +0900, Wonhyuk Yang wrote: > > > Because of 'min(1, ...)', fast_isolate_freepages set 'limit' > > > to 0 or 1. This takes away the opportunities of find candinate > > > pages. Also, even if 'limit' reaches zero, it scan once. It is > > > not consistent. So, modify the minimum value of 'limit' to 1. > > > > > > > The changelog could do with a little polish. > > > > In addition, what were the effects of this and what load did you use to > > evaluate it? While your patch is mostly correct, it has the potential > > side-effect of increasing system CPU usage in some cases and I'm curious > > to hear what you observed. Minimally it is worth noting in the changelog > > that there is a risk of increasing system CPU usage but that there are > > advantages too. Describe them in the changelog in case a regression > > bisects to your patch. > > I tested it on the thpscale and the results are as follows. > > 5.12 > 5.12 > vanilla > patched > Amean fault-both-1 598.15 ( 0.00%) 592.56 ( 0.93%) > Amean fault-both-3 1494.47 ( 0.00%) 1514.35 ( -1.33%) > Amean fault-both-5 2519.48 ( 0.00%) 2471.76 ( 1.89%) > Amean fault-both-7 3173.85 ( 0.00%) 3079.19 ( 2.98%) > Amean fault-both-12 8063.83 ( 0.00%) 7858.29 ( 2.55%) > Amean fault-both-18 8781.20 ( 0.00%) 7827.70 * 10.86%* > Amean fault-both-24 12576.44 ( 0.00%) 12250.20 ( 2.59%) > Amean fault-both-30 18503.27 ( 0.00%) 17528.11 * 5.27%* > Amean fault-both-32 16133.69 ( 0.00%) 13874.24 * 14.00%* > > > 5.12 5.12 > > vanilla patched > Ops Compaction migrate scanned 6547133.00 5963901.00 > Ops Compaction free scanned 32452453.00 26609101.00 > Ok, mention this in the changelog and maybe include the overall system CPU usage as well. It will be higher but should be acceptable. > One thing to worry about is that the results are very different every time. > Is there any precise way to measure this patch? > Not with this workload, it was designed to simply hammer compaction heavily to see if latencies were unacceptably high and also for tracing various compaction corner cases. > > > @@ -1456,7 +1456,7 @@ fast_isolate_freepages(struct compact_control *cc) > > > high_pfn = pfn; > > > > > > /* Shorten the scan if a candidate is found */ > > > - limit >>= 1; > > > + limit = max(1U, limit >> 1); > > > } > > > > > > if (order_scanned >= limit) > > > > This hunk should be dropped. Once a candidate free page has been > > identified, it's ok to decay the limit to 0. This hunk introduces a risk > > of increasing system CPU usage unnecessarily. > > Yes, you are right. I'll take your opinion. > Thanks. > > > @@ -1496,7 +1496,7 @@ fast_isolate_freepages(struct compact_control *cc) > > > * to freelist_scan_limit. > > > */ > > > if (order_scanned >= limit) > > > - limit = min(1U, limit >> 1); > > > + limit = max(1U, limit >> 1); > > > } > > > > The change is fine but I have a minor nitpick that you are free to > > ignore. The comment above this block has a typo. > > > > s/scan ig related/scan is related/ > > > > Ordinarily patches to fix spelling are ignored but you are altering this > > area anyway and it's helpful to see the full comment when reviewing this > > patch. I think it would be harmless to fix the spelling in the context > > of this patch. > > Okay, I'll fix this as well. > > Thank you for your review. No problem, thank you for the patch. Please cc me on v2 and I'll rerun some tests just to be sure before acking it. -- Mel Gorman SUSE Labs
