On Mon, 2 Feb 2015 16:55:25 +0000 Mel Gorman <mgorman@xxxxxxx> wrote: > glibc malloc changed behaviour in glibc 2.10 to have per-thread arenas > instead of creating new areans if the existing ones were contended. > The decision appears to have been made so the allocator scales better but the > downside is that madvise(MADV_DONTNEED) is now called for these per-thread > areans during free. This tears down pages that would have previously > remained. There is nothing wrong with this decision from a functional point > of view but any threaded application that frequently allocates/frees the > same-sized region is going to incur the full teardown and refault costs. MADV_DONTNEED has been there for many years. How could this problem not have been noticed during glibc 2.10 development/testing? Is there some more recent kernel change which is triggering this? > This patch identifies when a thread is frequently calling MADV_DONTNEED > on the same region of memory and starts ignoring the hint. That's pretty nasty-looking :( And presumably there are all sorts of behaviours which will still trigger the problem but which will avoid the start/end equality test in ignore_madvise_hint()? Really, this is a glibc problem and only a glibc problem. MADV_DONTNEED is unavoidably expensive and glibc is calling MADV_DONTNEED for a region which it *does* need. Is there something preventing this from being addressed within glibc? -- 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>