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    SubjectRe: [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files
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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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