Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments | Date | Mon, 2 Feb 2009 23:10:42 +0900 (JST) |
| |
(cc to mel)
> On Mon, 2 Feb 2009, KOSAKI Motohiro wrote: > > > > > > - if (flags & MAP_NORESERVE) > > > + /* > > > + * Set 'VM_NORESERVE' if we should not account for the > > > + * memory use of this mapping. We only honor MAP_NORESERVE > > > + * if we're allowed to overcommit memory. > > > + */ > > > + if ((flags & MAP_NORESERVE) && sysctl_overcommit_memory != OVERCOMMIT_NEVER) > > > > I afraid this line a bit. > > if following scenario happend, we can lost VM_NORESERVE? > > > > 1. admin set overcommit_memory to "never" > > 2. mmap > > 3. admin set overcommit_memory to "guess" > > I still haven't reviewed it fully myself (and note that what > Linus put in his tree is not identical to this posted patch), > but I do believe this is okay. > > When admin changes overcommit_memory, we don't make a pass across > every vma of every mm in the system, to adjust all the accounting > of VM_NORESERVE areas; so I think it's quite reasonable to take > VM_NORESERVE as reflecting the policy in force when that vma was > created. And nothing is displaying the VM_NORESERVE flag.
hmhm, I see.
> Ah, you're actually thinking of > 4. mprotect > with the original flags (!VM_WRITE) such that no VM_ACCOUNT was done, > and now VM_WRITE is added and the accounting is done despite it having > been mapped MAP_NORESERVE originally. Whereas before Linus's change, > VM_NORESERVE would have still exempted it. > > Well... I don't think I care!
Yeah.
FWIW, we don't need VM_NORESERVE checking now because VM_NORESERVE and VM_ACCOUNT are exclusive condition now :)
> But I wonder what the hugetlb situation is: that > if (!accountable) > vm_flags |= VM_NORESERVE; > looks suspicious to me, they look as if they're exempting all > the hugetlb pages from its accounting, whereas !accountable was > only supposed to exempt them from mmap_region()'s own accounting.
HAHAHA, Indeed.
when hugepage shared read-only mapping -> hugepage shared writable maping, following code seems to cause calling vm_enough_memory() although hugepage.
======================================================== mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev, unsigned long start, unsigned long end, unsigned long newflags) { if (newflags & VM_WRITE) { if (!(oldflags & (VM_ACCOUNT|VM_WRITE| VM_SHARED|VM_NORESERVE))) { charged = nrpages; if (security_vm_enough_memory(charged)) return -ENOMEM; newflags |= VM_ACCOUNT; } } ==========================================================
mel, what do you think this?
> > Perhaps. I'm still looking at other things, > not given this the time it needs yet. > > Hugh
| |