lkml.org 
[lkml]   [2007]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [patch 2/3] MAP_NOZERO - implement sys_brk2()
    On 6/27/07, Hugh Dickins <hugh@veritas.com> wrote:
    > Not so: if an mmap can be done by extending either adjacent vma (prot
    > and flags and file and offset all match up), that's what's done and no
    > separate vma is created. (And adjacent vmas get merged when mprotect
    > removes the difference in protection.)

    mmap return values are randomized. If they would be mergable
    something would be wrong.


    > I don't think there's any such reason to prefer brk to mmap.

    Talk to the Quadrics people. Some of their interconnect adapters
    incur significant costs with separate VMAs.


    > Please let me know if you've a test case which shows more vmas than
    > expected.

    Not related to this, but we already have "too many" VMAs for some
    definition of "too many". Since we split VMA when the protection
    changes each thread stack consists at least of two VMA (three for
    ia64). There was an approach at some point to push the access flags
    down and allow VMAs to stretch further. Why was this deemed
    unsuitable? It could have quite a bit with situations with many
    threads (Java). As I've told back when this came up, we had one
    customer where the VMA lookup actually showed up in profiles.
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-06-27 19:05    [W:3.349 / U:0.068 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site