From: Matthew Wilcox <willy@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>, Jann Horn <jannh@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
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SeongJae Park <sj@kernel.org>,
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Subject: Re: [PATCH mm-unstable] mm/khugepaged: fix collapse_pte_mapped_thp() versus uffd
Date: Tue, 22 Aug 2023 19:45:41 +0100 [thread overview]
Message-ID: <ZOUCVRxM8aPH6fva@casper.infradead.org> (raw)
In-Reply-To: <1b7c7056-d742-86bf-fec-fdb024b2381@google.com>
On Tue, Aug 22, 2023 at 11:34:19AM -0700, Hugh Dickins wrote:
> (Yes, the locking is a bit confusing: but mainly for the unrelated reason,
> that with the split locking configs, we never quite know whether this lock
> is the same as that lock or not, and so have to be rather careful.)
Is it time to remove the PTE split locking config option? I believe all
supported architectures have at least two levels of page tables, so if we
have split ptlocks, ptl and pml are always different from each other (it's
just that on two level machines, pmd == pud == p4d == pgd). With huge
thread counts now being the norm, it's hard to see why anybody would want
to support SMP and !SPLIT_PTE_PTLOCKS. To quote the documentation ...
Split page table lock for PTE tables is enabled compile-time if
CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS.
If split lock is disabled, all tables are guarded by mm->page_table_lock.
You can barely buy a wrist-watch without eight CPUs these days.
next prev parent reply other threads:[~2023-08-22 18:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-21 19:51 Hugh Dickins
2023-08-21 21:26 ` Peter Xu
2023-08-21 21:59 ` Jann Horn
2023-08-22 2:51 ` Hugh Dickins
2023-08-22 14:31 ` Peter Xu
2023-08-22 18:34 ` Hugh Dickins
2023-08-22 18:45 ` Matthew Wilcox [this message]
2023-08-22 19:10 ` Hugh Dickins
2023-08-22 14:39 ` Jann Horn
2023-08-22 15:22 ` Matthew Wilcox
2023-08-22 15:30 ` Jann Horn
2023-08-22 15:33 ` David Hildenbrand
2023-08-22 15:28 ` David Hildenbrand
2023-08-22 18:54 ` Hugh Dickins
2023-08-22 19:07 ` Jann Horn
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