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@xxxxxxxxxxxxxxxxx/
