[Bug 281471] ASLR: jemalloc RES memory keeps on increasing until process cores

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=281471

Brooks Davis <brooks@FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |brooks@FreeBSD.org

--- Comment #3 from Brooks Davis <brooks@FreeBSD.org> ---
There was a commit in June to reduce jemalloc induced fragmentation which
describes a somewhat different scenerio.  It has not been merged to any
non-main branch, but might be relevant?

commit 268f19aacc6af8f64c438e8515213023a2e66ed7
Author: Alan Cox <alc@FreeBSD.org>
Date:   Sun Jun 9 11:58:27 2024 -0500

    vm: Reduce address space fragmentation

    jemalloc performs two types of virtual memory allocations: (1) large
    chunks of virtual memory, where the chunk size is a multiple of a
    superpage and explicitly aligned, and (2) small allocations, mostly
    128KB, where no alignment is requested.  Typically, it starts with a
    small allocation, and over time it makes both types of allocation.

    With anon_loc being updated on every allocation, we wind up with a
    repeating pattern of a small allocation, a large gap, and a large,
    aligned allocation.  (As an aside, we wind up allocating a reservation
    for these small allocations, but it will never fill because the next
    large, aligned allocation updates anon_loc, leaving a gap that will
    never be filled with other small allocations.)

    With this change, anon_loc isn't updated on every allocation.  So, the
    small allocations will be clustered together, the large allocations will
    be clustered together, and there will be fewer gaps between the
    anonymous memory allocations.  In addition, I see a small reduction in
    reservations allocated (e.g., 1.6% during buildworld), fewer partially
    populated reservations, and a small increase in 64KB page promotions on
    arm64.

    Reviewed by:    kib
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D39845

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