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    SubjectRe: [PATCH] VM accounting 1/3 trivial
    On 23 Jul 2002, Alan Cox wrote:
    > On Tue, 2002-07-23 at 18:27, Hugh Dickins wrote:
    > > First of three patches against 2.4.19-rc3-ac3 fixing some VM accounting.
    > > Could be split further, but this one too trivial to need much thought.
    > >
    > > 1. do_munmap doesn't need an extra acct arg (and rc3-ac3 still leaves
    > > arch files without it): just clear VM_ACCOUNT in mremap's move_vma.
    > Are you sure that is correct. I started off on that basis but never got
    > it to work reliably when mremap changes multiple vmas ?

    Thank you, it is surely incorrect (in the case where the do_munmap does
    not cover the whole vma, leaving one or two pieces behind: I think that
    must be the case you're remembering). Would a patch which (if necessary)
    reapplies VM_ACCOUNT to the leftover piece(s) be welcome, or would it
    just look like an ugly face-saving exercise?

    > Can you split out items #2, #4 first of all and submit those alone, then
    > I can review each item on its own and run vm_validate tests

    Okay, will do, thanks. And you will also ignore patches 2/3, 3/3 now,
    since David has given a clear vote for more MAP_NORESERVE consistency,
    and VM_NORESERVE would be more natural to pass from do_mmap_pgoff to
    shmem_file_setup than my VM_SHARED|VM_ACCOUNT abuse.

    But I'll still have a consistency problem with MAP_NORESERVE versus
    sysctl_overcommit_memory, when the latter is changed (> 1 or <= 1).
    The closest I can get to a consistent position is that do_mmap_pgoff
    only sets VM_NORESERVE if MAP_NORESERVE and sysctl_overcommit_memory
    <= 1 (as you wish), but that thereafter (in mprotect and in mremap,
    even when extending the mapping) VM_NORESERVE will be respected (and
    propagated when splitting) even while sysctl_overcommit_memory > 1.
    Mirroring the vice versa situation, of the reservations made when
    MAP_NORESERVE is ignored, and thereafter.

    You might prefer more draconian enforcment, but I fear it
    could behave strangely. Does the above sound fair to you?


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