From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Qi Zheng <zhengqi.arch@bytedance.com>,
Yang Shi <shy828301@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Xu <peterx@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
Alistair Popple <apopple@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Ira Weiny <ira.weiny@intel.com>,
Steven Price <steven.price@arm.com>,
SeongJae Park <sj@kernel.org>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Huang Ying <ying.huang@intel.com>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Zack Rusin <zackr@vmware.com>, Jason Gunthorpe <jgg@ziepe.ca>,
Axel Rasmussen <axelrasmussen@google.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Minchan Kim <minchan@kernel.org>,
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Russell King <linux@armlinux.org.uk>,
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"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Jann Horn <jannh@google.com>,
Vishal Moola <vishal.moola@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
linux-arm-kernel@lists.infradead.org, sparclinux@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page
Date: Tue, 20 Jun 2023 00:47:54 -0700 (PDT) [thread overview]
Message-ID: <5cd9f442-61da-4c3d-eca-b7f44d22aa5f@google.com> (raw)
In-Reply-To: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com>
Add powerpc-specific pte_free_defer(), to call pte_free() via call_rcu().
pte_free_defer() will be called inside khugepaged's retract_page_tables()
loop, where allocating extra memory cannot be relied upon. This precedes
the generic version to avoid build breakage from incompatible pgtable_t.
This is awkward because the struct page contains only one rcu_head, but
that page may be shared between PTE_FRAG_NR pagetables, each wanting to
use the rcu_head at the same time: account concurrent deferrals with a
heightened refcount, only the first making use of the rcu_head, but
re-deferring if more deferrals arrived during its grace period.
Signed-off-by: Hugh Dickins <hughd@google.com>
---
arch/powerpc/include/asm/pgalloc.h | 4 +++
arch/powerpc/mm/pgtable-frag.c | 51 ++++++++++++++++++++++++++++++
2 files changed, 55 insertions(+)
diff --git a/arch/powerpc/include/asm/pgalloc.h b/arch/powerpc/include/asm/pgalloc.h
index 3360cad78ace..3a971e2a8c73 100644
--- a/arch/powerpc/include/asm/pgalloc.h
+++ b/arch/powerpc/include/asm/pgalloc.h
@@ -45,6 +45,10 @@ static inline void pte_free(struct mm_struct *mm, pgtable_t ptepage)
pte_fragment_free((unsigned long *)ptepage, 0);
}
+/* arch use pte_free_defer() implementation in arch/powerpc/mm/pgtable-frag.c */
+#define pte_free_defer pte_free_defer
+void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable);
+
/*
* Functions that deal with pagetables that could be at any level of
* the table need to be passed an "index_size" so they know how to
diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c
index 20652daa1d7e..e4f58c5fc2ac 100644
--- a/arch/powerpc/mm/pgtable-frag.c
+++ b/arch/powerpc/mm/pgtable-frag.c
@@ -120,3 +120,54 @@ void pte_fragment_free(unsigned long *table, int kernel)
__free_page(page);
}
}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define PTE_FREE_DEFERRED 0x10000 /* beyond any PTE_FRAG_NR */
+
+static void pte_free_now(struct rcu_head *head)
+{
+ struct page *page;
+ int refcount;
+
+ page = container_of(head, struct page, rcu_head);
+ refcount = atomic_sub_return(PTE_FREE_DEFERRED - 1,
+ &page->pt_frag_refcount);
+ if (refcount < PTE_FREE_DEFERRED) {
+ pte_fragment_free((unsigned long *)page_address(page), 0);
+ return;
+ }
+ /*
+ * One page may be shared between PTE_FRAG_NR pagetables.
+ * At least one more call to pte_free_defer() came in while we
+ * were already deferring, so the free must be deferred again;
+ * but just for one grace period, however many calls came in.
+ */
+ while (refcount >= PTE_FREE_DEFERRED + PTE_FREE_DEFERRED) {
+ refcount = atomic_sub_return(PTE_FREE_DEFERRED,
+ &page->pt_frag_refcount);
+ }
+ /* Remove that refcount of 1 left for fragment freeing above */
+ atomic_dec(&page->pt_frag_refcount);
+ call_rcu(&page->rcu_head, pte_free_now);
+}
+
+void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
+{
+ struct page *page;
+
+ page = virt_to_page(pgtable);
+ /*
+ * One page may be shared between PTE_FRAG_NR pagetables: only queue
+ * it once for freeing, but note whenever the free must be deferred.
+ *
+ * (This would be much simpler if the struct page had an rcu_head for
+ * each fragment, or if we could allocate a separate array for that.)
+ *
+ * Convert our refcount of 1 to a refcount of PTE_FREE_DEFERRED, and
+ * proceed to call_rcu() only when the rcu_head is not already in use.
+ */
+ if (atomic_add_return(PTE_FREE_DEFERRED - 1, &page->pt_frag_refcount) <
+ PTE_FREE_DEFERRED + PTE_FREE_DEFERRED)
+ call_rcu(&page->rcu_head, pte_free_now);
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
--
2.35.3
next prev parent reply other threads:[~2023-06-20 7:49 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-20 7:35 [PATCH v2 00/12] mm: free retracted page table by RCU Hugh Dickins
2023-06-20 7:40 ` [PATCH v2 01/12] mm/pgtable: add rcu_read_lock() and rcu_read_unlock()s Hugh Dickins
2023-06-20 7:42 ` [PATCH v2 02/12] mm/pgtable: add PAE safety to __pte_offset_map() Hugh Dickins
2023-06-20 7:43 ` [PATCH v2 03/12] arm: adjust_pte() use pte_offset_map_nolock() Hugh Dickins
2023-06-20 7:45 ` [PATCH v2 04/12] powerpc: assert_pte_locked() " Hugh Dickins
2023-06-20 7:47 ` Hugh Dickins [this message]
2023-06-20 11:45 ` [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page Jason Gunthorpe
2023-06-20 19:54 ` Hugh Dickins
2023-06-20 23:52 ` Jason Gunthorpe
2023-06-22 2:36 ` Hugh Dickins
2023-06-27 17:01 ` Jason Gunthorpe
2023-06-27 20:53 ` Hugh Dickins
2023-06-20 7:49 ` [PATCH v2 06/12] sparc: add pte_free_defer() for pte_t *pgtable_t Hugh Dickins
2023-06-20 7:51 ` [PATCH v2 07/12] s390: add pte_free_defer() for pgtables sharing page Hugh Dickins
2023-06-28 19:16 ` Gerald Schaefer
2023-06-29 5:08 ` Hugh Dickins
2023-06-29 15:22 ` Jason Gunthorpe
2023-06-29 15:56 ` Gerald Schaefer
2023-06-30 6:00 ` Hugh Dickins
2023-07-02 4:32 ` Hugh Dickins
2023-07-04 13:40 ` Alexander Gordeev
2023-07-04 16:03 ` Hugh Dickins
2023-07-04 15:19 ` Gerald Schaefer
2023-07-04 17:03 ` Hugh Dickins
2023-07-05 12:55 ` Gerald Schaefer
2023-07-06 1:20 ` Hugh Dickins
2023-07-06 15:02 ` Gerald Schaefer
2023-07-06 19:45 ` Hugh Dickins
2023-07-10 17:21 ` Jason Gunthorpe
2023-07-05 6:46 ` Alexander Gordeev
2023-07-06 0:52 ` Hugh Dickins
2023-07-07 14:37 ` Gerald Schaefer
2023-07-03 16:10 ` Gerald Schaefer
2023-06-29 13:59 ` Alexander Gordeev
2023-06-29 15:43 ` Gerald Schaefer
2023-06-30 13:38 ` Claudio Imbrenda
2023-06-30 15:28 ` Hugh Dickins
2023-06-30 16:25 ` Claudio Imbrenda
2023-06-30 19:22 ` Hugh Dickins
2023-07-03 11:00 ` Claudio Imbrenda
2023-07-03 21:29 ` Jason Gunthorpe
2023-06-20 7:53 ` [PATCH v2 08/12] mm/pgtable: add pte_free_defer() for pgtable as page Hugh Dickins
2023-06-20 7:54 ` [PATCH v2 09/12] mm/khugepaged: retract_page_tables() without mmap or vma lock Hugh Dickins
2023-06-20 7:56 ` [PATCH v2 10/12] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock() Hugh Dickins
2023-06-20 8:04 ` [PATCH mm " Hugh Dickins
2023-06-20 7:58 ` [PATCH v2 11/12] mm/khugepaged: delete khugepaged_collapse_pte_mapped_thps() Hugh Dickins
2023-06-20 7:59 ` [PATCH v2 12/12] mm: delete mmap_write_trylock() and vma_try_start_write() Hugh Dickins
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