On Fri, Jun 21, 2013 at 10:12 PM, Kyungmin Park <kmpark@xxxxxxxxxxxxx> wrote: > On Sat, Jun 22, 2013 at 8:42 AM, Colin Cross <ccross@xxxxxxxxxx> wrote: >> One of the features of ashmem (drivers/staging/android/ashmem.c) that >> hasn't gotten much discussion about moving out of staging is named >> anonymous memory. >> >> In Android, ashmem is used for three different features, and most >> users of it only care about one feature at a time. One is volatile >> ranges, which John Stultz has been implementing. The second is >> anonymous shareable memory without having a world-writable tmpfs that >> untrusted apps could fill with files. The third and most heavily used >> feature within the Android codebase is named anonymous memory, where a >> region of anonymous memory can have a name associated with it that >> will show up in /proc/pid/maps. The Dalvik VM likes to use this > > Good to know it. I didn't know ashmem provides these features. > we are also discussing these requirement internally. and study how to > show who request these anon memory and which callback is used for it. > >> feature extensively, even for memory that will never be shared and >> could easily be allocated using an anonymous mmap, and even malloc has >> used it in the past. It provides an easy way to collate memory used >> for different purposes across multiple processes, which Android uses >> for its "dumpsys meminfo" and "librank" tools to determine how much >> memory is used for java heaps, JIT caches, native mallocs, etc. > Same requirement for app developers. they want to know what's the > meaning these anon memory is allocated and how to find out these anon > memory is allocated at their codes. >> >> I'd like to add this feature for anonymous mmap memory. I propose >> adding an madvise2(unsigned long start, size_t len_in, int behavior, >> void *ptr, size_t size) syscall and a new MADV_NAME behavior, which >> treats ptr as a string of length size. The string would be copied >> somewhere reusable in the kernel, or reused if it already exists, and >> the kernel address of the string would get stashed in a new field in >> struct vm_area_struct. Adjacent vmas would only get merged if the >> name pointer matched, and naming part of a mapping would split the >> mapping. show_map_vma would print the name only if none of the other >> existing names rules match. > Do you want to create new syscall? can it use current madvise and only > allow this feature at linux only? > As you know it's just hint and it doesn't break existing memory behaviors. The existing madvise syscall only takes a single int to modify the vma, which is not enough to pass a pointer to a string. -- 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>