Re: [PATCH] hugetlb: simplify hugetlb handling in follow_page_mask

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





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)."




[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux