On Tue, Feb 03, 2015 at 09:47:18AM +0000, Mel Gorman wrote: > On Mon, Feb 02, 2015 at 02:22:36PM -0800, Dave Hansen wrote: > > On 02/02/2015 08:55 AM, Mel Gorman wrote: > > > This patch identifies when a thread is frequently calling MADV_DONTNEED > > > on the same region of memory and starts ignoring the hint. On an 8-core > > > single-socket machine this was the impact on ebizzy using glibc 2.19. > > > > The manpage, at least, claims that we zero-fill after MADV_DONTNEED is > > called: > > > > It also claims that the kernel is free to ignore the advice. > > > > MADV_DONTNEED > > > Do not expect access in the near future. (For the time > > > being, the application is finished with the given range, so the kernel > > > can free resources > > > associated with it.) Subsequent accesses of pages in this > > > range will succeed, but will result either in reloading of the memory > > > contents from the > > > underlying mapped file (see mmap(2)) or zero-fill-on-demand > > > pages for mappings without an underlying file. > > > > So if we have anything depending on the behavior that it's _always_ > > zero-filled after an MADV_DONTNEED, this will break it. > > True. I'd be surprised if any application depended on that
IIUC, jemalloc depends on this[1]. [1] https://github.com/jemalloc/jemalloc/blob/dev/src/chunk_mmap.c#L117 -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
