Messages in this thread Patch in this message | | | Date | Fri, 2 Jul 2004 13:02:09 +0200 | From | Ingo Molnar <> | Subject | [patch] flexible-mmap-update.patch, 2.6.7-mm5 |
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* Hugh Dickins <hugh@veritas.com> wrote:
> I think it's wrong to interpret a large or rlim_infinite stack rlimit > as an inviolable request to reserve that much for the stack: it makes > much less VM available than bottom up, not what was intended. Perhaps > top down should go bottom up (instead of belly up) when it fails - but > I'd probably better leave that to Ingo.
Agreed. the attached flexible-mmap-update.patch (against 2.6.7-mm5) implements the following changes:
- fall back to the bottom-up layout if the stack can grow unlimited (if the stack ulimit has been set to RLIM_INFINITY)
- try the bottom-up allocator if the top-down allocator fails - this can utilize the hole between the true bottom of the stack and its ulimit, as a last-resort effort.
i've tested a number of failure scenarios with various ulimits and mmap sizes, and we now successfully allocate a VM area in all cases i tested.
Ingo
- fall back to the bottom-up layout if the stack can grow unlimited (if the stack ulimit has been set to RLIM_INFINITY)
- try the bottom-up allocator if the top-down allocator fails - this can utilize the hole between the true bottom of the stack and its ulimit, as a last-resort effort.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
--- linux/arch/i386/mm/mmap.c.orig +++ linux/arch/i386/mm/mmap.c @@ -55,9 +55,10 @@ void arch_pick_mmap_layout(struct mm_str { /* * Fall back to the standard layout if the personality - * bit is set: + * bit is set, or if the expected stack growth is unlimited: */ - if (current->personality & ADDR_COMPAT_LAYOUT) { + if ((current->personality & ADDR_COMPAT_LAYOUT) || + current->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) { mm->mmap_base = TASK_UNMAPPED_BASE; mm->get_unmapped_area = arch_get_unmapped_area; mm->unmap_area = arch_unmap_area; --- linux/mm/mmap.c.orig +++ linux/mm/mmap.c @@ -1074,13 +1074,13 @@ void arch_unmap_area(struct vm_area_stru * stack's low limit (the base): */ unsigned long -arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr, - unsigned long len, unsigned long pgoff, - unsigned long flags) +arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, + const unsigned long len, const unsigned long pgoff, + const unsigned long flags) { struct vm_area_struct *vma, *prev_vma; struct mm_struct *mm = current->mm; - unsigned long base = mm->mmap_base; + unsigned long base = mm->mmap_base, addr = addr0; int first_time = 1; /* requested length too big for entire address space */ @@ -1142,7 +1142,20 @@ fail: first_time = 0; goto try_again; } - return -ENOMEM; + /* + * A failed mmap() very likely causes application failure, + * so fall back to the bottom-up function here. This scenario + * can happen with large stack limits and large mmap() + * allocations. + */ + mm->free_area_cache = TASK_UNMAPPED_BASE; + addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags); + /* + * Restore the topdown base: + */ + mm->free_area_cache = base; + + return addr; } void arch_unmap_area_topdown(struct vm_area_struct *area)
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