Messages in this thread | | | Date | Tue, 22 Jan 2008 05:39:23 +0300 | From | "Anton Salikhmetov" <> | Subject | Re: [PATCH -v7 2/2] Update ctime and mtime for memory-mapped files |
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2008/1/22, Linus Torvalds <torvalds@linux-foundation.org>: > > > On Tue, 22 Jan 2008, Anton Salikhmetov wrote: > > > > /* > > + * Scan the PTEs for pages belonging to the VMA and mark them read-only. > > + * It will force a pagefault on the next write access. > > + */ > > +static void vma_wrprotect(struct vm_area_struct *vma) > > +{ > > + unsigned long addr; > > + > > + for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) { > > + spinlock_t *ptl; > > + pgd_t *pgd = pgd_offset(vma->vm_mm, addr); > > + pud_t *pud = pud_offset(pgd, addr); > > + pmd_t *pmd = pmd_offset(pud, addr); > > + pte_t *pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > > This is extremely expensive over bigger areas, especially sparsely mapped > ones (it does all the lookups for all four levels over and over and over > again for eachg page). > > I think Peter Zijlstra posted a version that uses the regular kind of > nested loop (with inline functions to keep the thing nice and clean), > which gets rid of that.
Thanks for your feedback, Linus!
I will use Peter Zijlstra's version of such an operation in my next patch series.
> > [ The sad/funny part is that this is all how we *used* to do msync(), back > in the days: we're literally going back to the "pre-cleanup" logic. See > commit 204ec841fbea3e5138168edbc3a76d46747cc987: "mm: msync() cleanup" > for details ] > > Quite frankly, I really think you might be better off just doing a > > git revert 204ec841fbea3e5138168edbc3a76d46747cc987 > > and working from there! I just checked, and it still reverts cleanly, and > you'd end up with a nice code-base that (a) has gotten years of testing > and (b) already has the looping-over-the-pagetables code. > > Linus >
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