Messages in this thread | | | Date | Thu, 1 Sep 2022 18:40:26 +0800 | Subject | Re: [PATCH] hugetlb: simplify hugetlb handling in follow_page_mask | From | Baolin Wang <> |
| |
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)."
| |