On Fri, Jul 12, 2013 at 10:13:48AM +0200, Peter Zijlstra wrote: > 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is no longer valid all or part of the name will be replaced 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. In fact, nowhere in his entire Changelog does he explain why this needs be in the kernel; _why_ can't userspace do this? He needs to go change his allocators to use the new madv syscall anyway, he might as well change them to write the stuff to a local file and be done with it. what gives? -- 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>