On Tue, 29 Dec 2015 00:10:15 +0300 Cyrill Gorcunov <[email protected]> wrote:
> When inspecting a vague code inside prctl(PR_SET_MM_MEM)
> call (which testing the RLIMIT_DATA value to figure out
> if we're allowed to assign new @start_brk, @brk, @start_data,
> @end_data from mm_struct) it's been commited that RLIMIT_DATA
> in a form it's implemented now doesn't do anything useful
> because most of user-space libraries use mmap() syscall
> for dynamic memory allocations.
>
> Linus suggested to convert RLIMIT_DATA rlimit into something
> suitable for anonymous memory accounting. But in this patch
> we go further, and the changes are bundled together as:
>
> * keep vma counting if CONFIG_PROC_FS=n, will be used for limits
> * replace mm->shared_vm with better defined mm->data_vm
> * account anonymous executable areas as executable
> * account file-backed growsdown/up areas as stack
> * drop struct file* argument from vm_stat_account
> * enforce RLIMIT_DATA for size of data areas
>
> This way code looks cleaner: now code/stack/data
> classification depends only on vm_flags state:
>
> VM_EXEC & ~VM_WRITE -> code (VmExe + VmLib in proc)
> VM_GROWSUP | VM_GROWSDOWN -> stack (VmStk)
> VM_WRITE & ~VM_SHARED & !stack -> data (VmData)
>
> The rest (VmSize - VmData - VmStk - VmExe - VmLib) could be
> called "shared", but that might be strange beast like
> readonly-private or VM_IO area.
>
> - RLIMIT_AS limits whole address space "VmSize"
> - RLIMIT_STACK limits stack "VmStk" (but each vma individually)
> - RLIMIT_DATA now limits "VmData"
This clashes with
mm-mmapc-remove-redundant-local-variables-for-may_expand_vm.patch,
below. I resolved it thusly:
bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
{
if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
return false;
if ((flags & (VM_WRITE | VM_SHARED | (VM_STACK_FLAGS &
(VM_GROWSUP | VM_GROWSDOWN)))) == VM_WRITE)
return mm->data_vm + npages <= rlimit(RLIMIT_DATA);
return true;
}
From: Chen Gang <[email protected]>
Subject: mm/mmap.c: remove redundant local variables for may_expand_vm()
Simplify may_expand_vm()
[[email protected]: further simplification, per Naoya Horiguchi]
Signed-off-by: Chen Gang <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/mmap.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
diff -puN mm/mmap.c~mm-mmapc-remove-redundant-local-variables-for-may_expand_vm
mm/mmap.c
--- a/mm/mmap.c~mm-mmapc-remove-redundant-local-variables-for-may_expand_vm
+++ a/mm/mmap.c
@@ -2988,14 +2988,7 @@ out:
*/
int may_expand_vm(struct mm_struct *mm, unsigned long npages)
{
- unsigned long cur = mm->total_vm; /* pages */
- unsigned long lim;
-
- lim = rlimit(RLIMIT_AS) >> PAGE_SHIFT;
-
- if (cur + npages > lim)
- return 0;
- return 1;
+ return mm->total_vm + npages <= rlimit(RLIMIT_AS) >> PAGE_SHIFT;
}
static int special_mapping_fault(struct vm_area_struct *vma,
_
--
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