Messages in this thread | | | Date | Wed, 31 Aug 2022 09:07:28 +0800 | Subject | Re: [PATCH] hugetlb: simplify hugetlb handling in follow_page_mask | From | Baolin Wang <> |
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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.
[1] https://lore.kernel.org/all/cover.1661240170.git.baolin.wang@linux.alibaba.com/
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