Hello, On (09/05/16 11:18), Minchan Kim wrote: [..] > If I understand Sergey's point right, he means there is no gain > to save memory between before and after. > > With your approach, you can prevent unnecessary pageout(i.e., > uncompressible page swap out) but it doesn't mean you save the > memory compared to old so why does your patch decrease the number of > lowmemory killing? you are right Minchan, that was exactly my point. every compressed page that does not end up in huge_object zspage should result in some memory saving (somewhere in the range from bytes to kilobytes). > A thing I can imagine is without this feature, zram could be full of > uncompressible pages so good-compressible page cannot be swapped out. a good theory. in general, a selective compression of N first pages that fall under the given compression limit is not the same as a selective compression of N "best" compressible pages. so I'm a bit uncertain about the guarantees that the patch can provide. let's assume the following case. - zram compression size limit set to 2400 bytes (only pages smaller than that will be stored in zsmalloc) - first K pages to swapout have compression size of 2350 +/- 10% - next L pages have compression size of 2500 +/- 10% - last M pages are un-compressible - PAGE_SIZE. - zram disksize can fit N pages - N > K + L so instead of compressing and swapping out K + L pages, you would compress only K pages, leaving (L + M) * PAGE_SIZE untouched. thus I'd say that we might have bigger chances of LMK/OOM/etc. in some cases. -ss -- 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>