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    SubjectRe: [PATCH 0/3] ARM 4Kstacks: introduction
    From
    Hi,

    On Sat, Oct 22, 2011 at 9:36 PM, Russell King - ARM Linux
    <linux@arm.linux.org.uk> wrote:
    > On Sat, Oct 22, 2011 at 04:50:15PM +0800, Ming Lei wrote:
    >> On Wed, Oct 19, 2011 at 6:51 PM, Arnd Bergmann <arnd@arndb.de> wrote:
    >> > On Tuesday 18 October 2011 17:26:44 Tim Bird wrote:
    >> >> Even inside Sony, usage of 4K stacks is limited
    >> >> to some very special cases, where memory is exceedingly
    >> >> tight (we have one system with 4M of RAM).  And we
    >> >> don't mind lopping off features or coding around
    >> >> problem areas to support our special case.
    >> >
    >> > I would imagine that in those cases, you can gain more by reducing the
    >> > number of threads in the system. What is the highest number of
    >> > concurrent threads that you expect in a limited use case with no
    >> > networking or block devices?
    >>
    >> If system run for some time, sometimes it may be difficult for
    >> memory allocator to allocate 2 continuous page frames even  there are
    >> many spare page frames in system because of
    >> fragment issue, so the patch does make sense.
    >
    > If memory fragmentation is an issue for this, it probably means that we
    > need to switch to a software page size of 8K (or maybe 16K) rather than
    > stick with the hardware 4K size.  That would be a much more reliable
    > solution, especially as the L1 page table is 16K (if you're suffering
    > from memory fragmentation, the first thing which'd get you is the L1
    > page table allocation, not the kernel stack allocation.)

    If large page size is taken, memory utilization will be decreased a lot, so
    may cause some low memory system not workable at all.

    >> Anyway, it provides one option for user to apply 4k stack to avoid
    >> such kind of process creation failure.
    >
    > I refer you to the comments made by people who've tried running with 4K
    > stacks on x86, and their _vast_ experience of doing this.  If they say
    > that it causes stack overflows, then it's a problem.

    Stack overflow depends on code running path. For some low memory
    and simple application, the code path is not deep as x86, so providing
    a option of enabling 4K stack still makes sense for this kind of case or
    application.


    thanks,
    --
    Ming Lei
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