On 9/1/2022 2:59 PM, David Hildenbrand wrote:
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.
But from stable-kernel-rules, we should follow "It or an equivalent fix must already exist in Linus' tree (upstream)."
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