Messages in this thread |  | | | Subject | Re: RFC: Cleanup / small fixes to hugetlb fault handling | | From | Adam Litke <> | | Date | Wed, 26 Oct 2005 16:46:16 -0500 |
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On Wed, 2005-10-26 at 12:48 +1000, David Gibson wrote: > On Wed, Oct 26, 2005 at 12:00:55PM +1000, David Gibson wrote: > > Hi, Adam, Bill, Hugh, > > > > Does this look like a reasonable patch to send to akpm for -mm. > > Ahem. Or rather this version, which actually compiles. > > This patch makes some slight tweaks / cleanups to the fault handling > path for huge pages in -mm. My main motivation is to make it simpler > to fit COW in, but along the way it addresses a few minor problems > with the existing code: > > - The check against i_size was duplicated: once in > find_lock_huge_page() and again in hugetlb_fault() after taking the > page_table_lock. We only really need the locked one, so remove the > other.
Fair enough.
> - find_lock_huge_page() didn't, in fact, lock the page if it newly > allocated one, rather than finding it in the page cache already. As > far as I can tell this is a bug, so the patch corrects it.
Thanks. I was about to post a fix for this too. It is reproducible in the case where two threads race in the fault handler and both do alloc_huge_page(). In that case, the loser will fail to insert his page into the page cache and will call put_page() which has a BUG_ON(page_count(page) == 0).
> - find_lock_huge_page() isn't a great name, since it does extra things > not analagous to find_lock_page(). Rename it > find_or_alloc_huge_page() which is closer to the mark.
I'll agree with the above. I am not all that committed to the current layout and what you have here is a little closer to the thinking in my original patch ;)
<snip>
> +int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > + unsigned long address, int write_access) > +{ > + pte_t *ptep; > + pte_t entry; > + > + ptep = huge_pte_alloc(mm, address); > + if (! ptep) > + /* OOM */ > + return VM_FAULT_SIGBUS; > + > + entry = *ptep; > + > + if (pte_none(entry)) > + return hugetlb_no_page(mm, vma, address, ptep); > + > + /* we could get here if another thread instantiated the pte > + * before the test above */ > + > + return VM_FAULT_SIGBUS; > }
I'll agree with Ken that the last return should probably still be VM_FAULT_MINOR.
-- Adam Litke - (agl at us.ibm.com) IBM Linux Technology Center
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