On 01.09.22 03:24, Baolin Wang wrote: > > > On 9/1/2022 8:00 AM, Mike Kravetz wrote: >> On 08/31/22 09:07, Baolin Wang wrote: >>> >>> >>> On 8/31/2022 2:39 AM, Mike Kravetz wrote: >>>> On 08/30/22 09:44, Mike Kravetz wrote: >>>>> On 08/30/22 09:06, Baolin Wang wrote: >>>>>> Hi Mike, >>>>>> >>>>>> On 8/30/2022 7:40 AM, Mike Kravetz wrote: >>>>>>> During discussions of this series [1], it was suggested that hugetlb >>>>>>> handling code in follow_page_mask could be simplified. At the beginning >>>>>>> of follow_page_mask, there currently is a call to follow_huge_addr which >>>>>>> 'may' handle hugetlb pages. ia64 is the only architecture which provides >>>>>>> a follow_huge_addr routine that does not return error. Instead, at each >>>>>>> level of the page table a check is made for a hugetlb entry. If a hugetlb >>>>>>> entry is found, a call to a routine associated with that entry is made. >>>>>>> >>>>>>> Currently, there are two checks for hugetlb entries at each page table >>>>>>> level. The first check is of the form: >>>>>>> if (p?d_huge()) >>>>>>> page = follow_huge_p?d(); >>>>>>> the second check is of the form: >>>>>>> if (is_hugepd()) >>>>>>> page = follow_huge_pd(). >>>>>>> >>>>>>> We can replace these checks, as well as the special handling routines >>>>>>> such as follow_huge_p?d() and follow_huge_pd() with a single routine to >>>>>>> handle hugetlb vmas. >>>>>>> >>>>>>> A new routine hugetlb_follow_page_mask is called for hugetlb vmas at the >>>>>>> beginning of follow_page_mask. hugetlb_follow_page_mask will use the >>>>>>> existing routine huge_pte_offset to walk page tables looking for hugetlb >>>>>>> entries. huge_pte_offset can be overwritten by architectures, and already >>>>>>> handles special cases such as hugepd entries. >>>>>> >>>>>> Could you also mention that this patch will fix the lock issue for >>>>>> CONT-PTE/PMD hugetlb by changing to use huge_pte_lock()? which will help >>>>>> people to understand the issue. >>>>> >>>>> Will update message in v2. Thanks for taking a look! >>>>> >>>> >>>> One additional thought, we 'may' need a separate patch to fix the locking >>>> issues that can be easily backported. Not sure this 'simplification' is >>>> a good backport candidate. >>> >>> Yes, that was my thought before, but David did not like adding more >>> make-legacy-cruft-happy code. >>> >>> So how about creating a series that contains 3 patches: picking up patch 1 >>> and patch 3 of my previous series [1], and your current patch? That means >>> patch 1 and patch 2 in this series can fix the lock issue explicitly and be >>> suitable to backport, meanwhile patch 3 (which is your current patch) will >>> cleanup the legacy code. >>> >> >> When I looked at patch 3, I was thinking the update follow_huge_pmd routine >> would work for the PTE level with a few more modifications. Perhaps, this is >> too ugly but it is a smaller set of changes for backport. >> >> Of course, this would be followed up with the simplification patch which >> removes all this code. > > Yes, looks more simple. I can send you a formal patch with your > suggestion, which can be added into your cleanup series. Thanks. As an alternative, we can have a stable-only version that does that. -- Thanks, David / dhildenb
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