Messages in this thread | | | Date | Tue, 18 Oct 2005 14:34:38 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH]: Handling spurious page fault for hugetlb region for 2.6.14-rc4-git5 |
| |
"Seth, Rohit" <rohit.seth@intel.com> wrote: > > Linus, > > [PATCH]: Handle spurious page fault for hugetlb region > > The hugetlb pages are currently pre-faulted. At the time of mmap of > hugepages, we populate the new PTEs. It is possible that HW has already cached > some of the unused PTEs internally.
What's an "unused pte"? One which maps a regular-sized page at the same virtual address? How can such a thing come about, and why isn't it already a problem for regular-sized pages? From where does the hardware prefetch the pte contents?
IOW: please tell us more about this hardware pte-fetcher.
> These stale entries never get a chance to > be purged in existing control flow.
I'd have thought that invalidating those ptes at mmap()-time would be a more consistent approach.
> This patch extends the check in page fault code for hugepages. Check if > a faulted address falls with in size for the hugetlb file backing it. We > return VM_FAULT_MINOR for these cases (assuming that the arch specific > page-faulting code purges the stale entry for the archs that need it).
Do you have an example of the code which does this purging?
> --- linux-2.6.14-rc4-git5-x86/include/linux/hugetlb.h 2005-10-18 13:14:24.879947360 -0700 > +++ b/include/linux/hugetlb.h 2005-10-18 13:13:55.711381656 -0700 > @@ -155,11 +155,24 @@ > { > file->f_op = &hugetlbfs_file_operations; > } > + > +static inline int valid_hugetlb_file_off(struct vm_area_struct *vma, > + unsigned long address) > +{ > + struct inode *inode = vma->vm_file->f_dentry->d_inode; > + loff_t file_off = address - vma->vm_start; > + > + file_off += (vma->vm_pgoff << PAGE_SHIFT); > + > + return (file_off < inode->i_size); > +}
I suppose we should use i_size_read() here.
> + if (valid_hugetlb_file_off(vma, address)) > + /* We get here only if there was a stale(zero) TLB entry > + * (because of HW prefetching). > + * Low-level arch code (if needed) should have already > + * purged the stale entry as part of this fault handling. > + * Here we just return. > + */
If the low-level code has purged the stale pte then it knows what's happening. Perhaps it shouldn't call into handle_mm_fault() at all? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |