From: David Hildenbrand <david@redhat.com>
To: Yin Fengwei <fengwei.yin@intel.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
Ryan Roberts <ryan.roberts@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Nick Piggin <npiggin@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org
Subject: Re: [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP
Date: Wed, 31 Jan 2024 11:30:56 +0100 [thread overview]
Message-ID: <d83309fa-4daa-430f-ae52-4e72162bca9a@redhat.com> (raw)
In-Reply-To: <2375481c-9d61-4f06-9f96-232f25b0e49b@intel.com>
On 31.01.24 03:30, Yin Fengwei wrote:
>
>
> On 1/29/24 22:32, David Hildenbrand wrote:
>> +static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
>> + unsigned long addr, pte_t *ptep, unsigned int nr, int full)
>> +{
>> + pte_t pte, tmp_pte;
>> +
>> + pte = ptep_get_and_clear_full(mm, addr, ptep, full);
>> + while (--nr) {
>> + ptep++;
>> + addr += PAGE_SIZE;
>> + tmp_pte = ptep_get_and_clear_full(mm, addr, ptep, full);
>> + if (pte_dirty(tmp_pte))
>> + pte = pte_mkdirty(pte);
>> + if (pte_young(tmp_pte))
>> + pte = pte_mkyoung(pte);
> I am wondering whether it's worthy to move the pte_mkdirty() and pte_mkyoung()
> out of the loop and just do it one time if needed. The worst case is that they
> are called nr - 1 time. Or it's just too micro?
I also thought about just indicating "any_accessed" or "any_dirty" using
flags to the caller, to avoid the PTE modifications completely. Felt a
bit micro-optimized.
Regarding your proposal: I thought about that as well, but my assumption
was that dirty+young are "cheap" to be set.
On x86, pte_mkyoung() is setting _PAGE_ACCESSED.
pte_mkdirty() is setting _PAGE_DIRTY | _PAGE_SOFT_DIRTY, but it also has
to handle the saveddirty handling, using some bit trickery.
So at least for pte_mkyoung() there would be no real benefit as far as I
can see (might be even worse). For pte_mkdirty() there might be a small
benefit.
Is it going to be measurable? Likely not.
Am I missing something?
Thanks!
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2024-01-31 10:31 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-29 14:32 [PATCH v1 0/9] mm/memory: optimize unmap/zap with PTE-mapped THP David Hildenbrand
2024-01-29 14:32 ` [PATCH v1 1/9] mm/memory: factor out zapping of present pte into zap_present_pte() David Hildenbrand
2024-01-30 8:13 ` Ryan Roberts
2024-01-30 8:41 ` David Hildenbrand
2024-01-30 8:46 ` Ryan Roberts
2024-01-30 8:49 ` David Hildenbrand
2024-01-29 14:32 ` [PATCH v1 2/9] mm/memory: handle !page case in zap_present_pte() separately David Hildenbrand
2024-01-30 8:20 ` Ryan Roberts
2024-01-29 14:32 ` [PATCH v1 3/9] mm/memory: further separate anon and pagecache folio handling in zap_present_pte() David Hildenbrand
2024-01-30 8:31 ` Ryan Roberts
2024-01-30 8:37 ` David Hildenbrand
2024-01-30 8:45 ` Ryan Roberts
2024-01-30 8:47 ` David Hildenbrand
2024-01-29 14:32 ` [PATCH v1 4/9] mm/memory: factor out zapping folio pte into zap_present_folio_pte() David Hildenbrand
2024-01-30 8:47 ` Ryan Roberts
2024-01-29 14:32 ` [PATCH v1 5/9] mm/mmu_gather: pass "delay_rmap" instead of encoded page to __tlb_remove_page_size() David Hildenbrand
2024-01-30 8:41 ` Ryan Roberts
2024-01-29 14:32 ` [PATCH v1 6/9] mm/mmu_gather: define ENCODED_PAGE_FLAG_DELAY_RMAP David Hildenbrand
2024-01-30 9:03 ` Ryan Roberts
2024-01-29 14:32 ` [PATCH v1 7/9] mm/mmu_gather: add __tlb_remove_folio_pages() David Hildenbrand
2024-01-30 9:21 ` Ryan Roberts
2024-01-30 9:33 ` David Hildenbrand
2024-01-29 14:32 ` [PATCH v1 8/9] mm/mmu_gather: add tlb_remove_tlb_entries() David Hildenbrand
2024-01-30 9:33 ` Ryan Roberts
2024-01-29 14:32 ` [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP David Hildenbrand
2024-01-30 9:08 ` David Hildenbrand
2024-01-30 9:48 ` Ryan Roberts
2024-01-31 10:21 ` David Hildenbrand
2024-01-31 10:31 ` Ryan Roberts
2024-01-31 11:13 ` David Hildenbrand
2024-01-31 2:30 ` Yin Fengwei
2024-01-31 10:30 ` David Hildenbrand [this message]
2024-01-31 10:43 ` Yin, Fengwei
2024-01-31 2:20 ` [PATCH v1 0/9] " Yin Fengwei
2024-01-31 10:16 ` David Hildenbrand
2024-01-31 10:26 ` Ryan Roberts
2024-01-31 14:08 ` Michal Hocko
2024-01-31 14:20 ` David Hildenbrand
2024-01-31 14:03 ` Michal Hocko
2024-01-31 10:43 ` David Hildenbrand
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