On Fri, Jul 12, 2013 at 08:39:14AM +0300, Pekka Enberg wrote: > On 07/12/2013 05:34 AM, Colin Cross wrote: > >Userspace processes often have multiple allocators that each do > >anonymous mmaps to get memory. When examining memory usage of > >individual processes or systems as a whole, it is useful to be > >able to break down the various heaps that were allocated by > >each layer and examine their size, RSS, and physical memory > >usage. > > > >This patch adds a user pointer to the shared union in > >vm_area_struct that points to a null terminated string inside > >the user process containing a name for the vma. vmas that > >point to the same address will be merged, but vmas that > >point to equivalent strings at different addresses will > >not be merged. > > > >Userspace can set the name for a region of memory by calling > >prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name); > >Setting the name to NULL clears it. > > > >The names of named anonymous vmas are shown in /proc/pid/maps > >as [anon:<name>] and in /proc/pid/smaps in a new "Name" field > >that is only present for named vmas. If the userspace pointer > >is no longer valid all or part of the name will be replaced > >with "<fault>". > > > >The idea to store a userspace pointer to reduce the complexity > >within mm (at the expense of the complexity of reading > >/proc/pid/mem) came from Dave Hansen. This results in no > >runtime overhead in the mm subsystem other than comparing > >the anon_name pointers when considering vma merging. The pointer > >is stored in a union with fieds that are only used on file-backed > >mappings, so it does not increase memory usage. > > > >Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx> > > Ingo, PeterZ, is this something worthwhile for replacing our > current JIT symbol hack with perf? I really don't see the point of this stuff; in fact I intensely dislike it as I don't think this is something the kernel needs to do at all. Why can't these allocators Collin talks about use file maps and/or write their own meta-data to file? He is after all only interested in Android and they have complete control over the entire userspace stack. I also don't see it helping with the JIT stuff; you still need to write out a file with symbol information, we still need to find the file. A less hacky solution for the entire JIT thing is you writing a proper ELF-DSO and mmap()'ing that :-) Storing a JIT specific userspace pointer in the VMA doesn't help with any of that. -- 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>