Messages in this thread | | | From | Rasmus Villemoes <> | Subject | Re: [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files | Date | Wed, 14 Jan 2015 15:13:44 +0100 |
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On Wed, Jan 14 2015, Calvin Owens <calvinowens@fb.com> wrote:
> Commit b76437579d1344b6 ("procfs: mark thread stack correctly in > proc/<pid>/maps") introduced logic to mark thread stacks with the > "[stack:%d]" marker in /proc/<pid>/maps. > > This causes reading /proc/<pid>/maps to take O(N^2) time, where N is > the number of threads sharing an address space, since each line of > output requires iterating over the VMA list looking for ranges that > correspond to the stack pointer in any task's register set. When > dealing with highly-threaded Java applications, reading this file can > take hours and trigger softlockup dumps. > > Eliminating the "[stack:%d]" marker is not a viable option since it's > been there for some time, and I don't see a way to do the stack check > more efficiently that wouldn't end up making the whole thing really > ugly.
Just thinking out loud: Could one simply mark a VMA as being used for stack during the clone call (is there room in vm_flags, or does VM_GROWSDOWN already tell the whole story?), and then write the TID into a new field in the VMA - I think one could make a union with vm_pgoff so as not to enlarge the structure.
This would allow eliminating the loop over tasks in vm_is_stack.
Rasmus
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