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Date: Tue, 20 Jun 2023 00:47:54 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Mike Rapoport <rppt@...nel.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Matthew Wilcox <willy@...radead.org>,
David Hildenbrand <david@...hat.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Qi Zheng <zhengqi.arch@...edance.com>,
Yang Shi <shy828301@...il.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Peter Xu <peterx@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
Alistair Popple <apopple@...dia.com>,
Ralph Campbell <rcampbell@...dia.com>,
Ira Weiny <ira.weiny@...el.com>,
Steven Price <steven.price@....com>,
SeongJae Park <sj@...nel.org>,
Lorenzo Stoakes <lstoakes@...il.com>,
Huang Ying <ying.huang@...el.com>,
Naoya Horiguchi <naoya.horiguchi@....com>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Zack Rusin <zackr@...are.com>, Jason Gunthorpe <jgg@...pe.ca>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Minchan Kim <minchan@...nel.org>,
Christoph Hellwig <hch@...radead.org>,
Song Liu <song@...nel.org>,
Thomas Hellstrom <thomas.hellstrom@...ux.intel.com>,
Russell King <linux@...linux.org.uk>,
"David Sc. Miller" <davem@...emloft.net>,
Michael Ellerman <mpe@...erman.id.au>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Jann Horn <jannh@...gle.com>,
Vishal Moola <vishal.moola@...il.com>,
Vlastimil Babka <vbabka@...e.cz>,
linux-arm-kernel@...ts.infradead.org, sparclinux@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing
page
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@...gle.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
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