On Tue, Jun 07, 2016 at 09:25:50AM +0900, Minchan Kim wrote: > Hi Johannes, > > Thanks for the nice work. I didn't read all patchset yet but the design > makes sense to me so it would be better for zram-based on workload > compared to as is. Thanks! > On Mon, Jun 06, 2016 at 03:48:27PM -0400, Johannes Weiner wrote: > > --- a/Documentation/sysctl/vm.txt > > +++ b/Documentation/sysctl/vm.txt > > @@ -771,14 +771,20 @@ with no ill effects: errors and warnings on these stats are suppressed.) > > > > swappiness > > > > -This control is used to define how aggressive the kernel will swap > > -memory pages. Higher values will increase agressiveness, lower values > > -decrease the amount of swap. A value of 0 instructs the kernel not to > > -initiate swap until the amount of free and file-backed pages is less > > -than the high water mark in a zone. > > +This control is used to define the relative IO cost of cache misses > > +between the swap device and the filesystem as a value between 0 and > > +200. At 100, the VM assumes equal IO cost and will thus apply memory > > +pressure to the page cache and swap-backed pages equally. At 0, the > > +kernel will not initiate swap until the amount of free and file-backed > > +pages is less than the high watermark in a zone. > > Generally, I agree extending swappiness value good but not sure 200 is > enough to represent speed gap between file and swap sotrage in every > cases. - Just nitpick. How so? You can't give swap more weight than 100%. 200 is the maximum possible value. > Some years ago, I extended it to 200 like your patch and experimented it > based on zram in our platform workload. At that time, it was terribly > slow in app switching workload if swappiness is higher than 150. > Although it was highly dependent on the workload, it's dangerous to > recommend it before fixing balacing between file and anon, I think. > IOW, I think this patch should be last one in this patchset. Good point. I'll tone down the recommendations. But OTOH it's a fairly trivial patch, so I wouldn't want it to close after the current 10/10. > > The default value is 60. > > > > +On non-rotational swap devices, a value of 100 (or higher, depending > > +on what's backing the filesystem) is recommended. > > + > > +For in-memory swap, like zswap, values closer to 200 are recommended. > > maybe, like zram > > I'm not sure it would be good suggestion for zswap because it ends up > writing cached pages to swap device once it reaches threshold. > Then, the cost is compression + decompression + write I/O which is > heavier than normal swap device(i.e., write I/O). OTOH, zram have no > (writeback I/O+ decompression) cost. Oh, good catch. Yeah, I'll change that for v2. Thanks for your input, Minchan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>