Until we have better performance numbers on the lazy reclaim path, we can just alias MADV_FREE to MADV_DONTNEED with this trivial patch. This way glibc can go ahead with the optimization on their side and we can figure out the kernel side later. Signed-off-by: Rik van Riel --- When I get back from the Red Hat Summit (Saturday), I will run more performance numbers with and without the lazy reclaiming of pages. Nick Piggin wrote: > Ulrich Drepper wrote: >> Nick Piggin wrote: >> >>> What I found is that, on this system, MADV_FREE performance improvement >>> was in the noise when you look at it on top of the MADV_DONTNEED glibc >>> and down_read(mmap_sem) patch in sysbench. >> >> >> I don't want to judge the numbers since I cannot but I want to make an >> observations: even if in the SMP case MADV_FREE turns out to not be a >> bigger boost then there is still the UP case to keep in mind where Rik >> measured a significant speed-up. As long as the SMP case isn't hurt >> this is reaosn enough to use the patch. With more and more cores on one >> processor SMP systems are pushed evermore to the high-end side. You'll >> find many installations which today use SMP will be happy enough with >> many-core UP machines. > > OK, sure. I think we need more numbers though. > > And even if this was a patch with _no_ possibility for regressions and it > was a completely trivial one that improves performance in some cases... > one big problem is that it uses another page flag. > > I literally have about 4 or 5 new page flags I'd like to add today :) I > can't of course, because we have very few spare ones left. > > From the MySQL numbers on this system, it seems like performance is in the > noise, and MADV_DONTNEED makes the _vast_ majority of the improvement. > This is also the case with Rik's benchmarks, and while he did see some > improvement, I found the runs to be quite variable, so it would be ideal > to get a larger sample. > > And the fact that the poor behaviour of the old style malloc/free went > unnoticed for so long indicates that it won't be the end of the world if > we didn't merge MADV_FREE right now. > -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic.