Messages in this thread | | | Date | Wed, 04 Apr 2012 13:59:03 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH RFC] mm: account VMA before forced-COW via /proc/pid/mem |
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Oleg Nesterov wrote: > On 04/02, Konstantin Khlebnikov wrote: >> >> Currently kernel does not account read-only private mappings into memory commitment. >> But these mappings can be force-COW-ed in get_user_pages(). > > Heh. tail -n3 Documentation/vm/overcommit-accounting > may be you should update it then.
I just wonder how fragile this accounting...
> > Can't really comment the patch, this is not my area. Still, > >> + down_write(&mm->mmap_sem); >> + *pvma = vma = find_vma(mm, addr); >> + if (vma&& vma->vm_start<= addr) { >> + ret = vma->vm_end - addr; >> + if ((vma->vm_flags& (VM_ACCOUNT | VM_NORESERVE | VM_SHARED | >> + VM_HUGETLB | VM_MAYWRITE)) == VM_MAYWRITE) { >> + if (!security_vm_enough_memory_mm(mm, vma_pages(vma))) > > Oooooh, the whole vma. Say, gdb installs the single breakpoint into > the huge .text mapping...
We cannot split vma right there, this will be really weird. =)
> > I am not sure, but probably you want to check at least VM_IO/PFNMAP > as well. We do not want to charge this memory and retry with FOLL_FORCE > before vm_ops->access(). Say, /dev/mem
No, VM_IO/PFNMAP aren't affect accounting, there is VM_NORESERVE for this.
> > Hmm. OTOH, if I am right then mprotect_fixup() should be fixed??
mprotect_fixup() does not account area if it already accounted, so all ok.
> > > We drop ->mmap_sem... Say, the task does mremap() in between and > len == 2 * PAGE_SIZE. Then, for example, copy_to_user_page() can > write to the same page twice. Perhaps not a problem in practice, > I dunno.
I have an old unfinished patch which implements upgrade_read() for rw-semaphore =)
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