Messages in this thread | | | Date | Thu, 1 Sep 2022 09:24:42 +0800 | Subject | Re: [PATCH] hugetlb: simplify hugetlb handling in follow_page_mask | From | Baolin Wang <> |
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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.
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