On Tue, Nov 25, 2014 at 08:19:40PM +0900, Chanho Min wrote: > > > The faultaround improves the file read performance, whereas pages which > > > can be dropped by drop_caches are reduced. On some systems, The amount of > > > freeable pages under memory pressure is more important than read > > > performance. > > > > The faultaround pages *are* freeable. Perhaps you meant "free" here. > > > > Please tell us a great deal about the problem which you are trying to > > solve. What sort of system, what sort of workload, what is bad about > > the behaviour which you are observing, etc. > > We are trying to solve two issues. > > We drop page caches by writing to /proc/sys/vm/drop_caches at specific point > and make suspend-to-disk image. The size of this image is increased if faultaround > is worked. drop_caches should never be used outside debugging process. If you use it as part of usual workflow you're doing something wrong. I'm not aware about details on how suspend-to-disk works, but I don't see much point in saving page cache pages into suspend-to-disk image. Dirty pages should be write out and we can read them back after resume on first use. Possible exception is mlocked pages. > Under memory pressure, we want to drop many page caches as possible. > But, The number of dropped pages are reduced compared to non-faultaround kernel. The reason why you see more pages in page cache after drop_pages with faultaround enabled is that drop_pages doesn't touch mapped pages. And with faultaround we obviously have more pages mapped. It's not a reason to have faultaround disable. You should take a closer look on suspend process. -- Kirill A. Shutemov -- 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>