From: David Hildenbrand <david@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Yang Shi <shy828301@gmail.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
Michal Hocko <mhocko@kernel.org>, Nadav Amit <namit@vmware.com>,
Rik van Riel <riel@surriel.com>, Roman Gushchin <guro@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Peter Xu <peterx@redhat.com>, Donald Dutile <ddutile@redhat.com>,
Christoph Hellwig <hch@lst.de>, Oleg Nesterov <oleg@redhat.com>,
Jan Kara <jack@suse.cz>, Liang Zhang <zhangliang5@huawei.com>,
Pedro Gomes <pedrodemargomes@gmail.com>,
Oded Gabbay <oded.gabbay@gmail.com>,
linux-mm@kvack.org, David Hildenbrand <david@redhat.com>
Subject: [PATCH v4 03/17] mm/memory: slightly simplify copy_present_pte()
Date: Thu, 28 Apr 2022 10:34:27 +0200 [thread overview]
Message-ID: <20220428083441.37290-4-david@redhat.com> (raw)
In-Reply-To: <20220428083441.37290-1-david@redhat.com>
Let's move the pinning check into the caller, to simplify return code
logic and prepare for further changes: relocating the
page_needs_cow_for_dma() into rmap handling code.
While at it, remove the unused pte parameter and simplify the comments a
bit.
No functional change intended.
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/memory.c | 53 ++++++++++++++++-------------------------------------
1 file changed, 16 insertions(+), 37 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 76e3af9639d9..ca0b256d1065 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -862,19 +862,11 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
}
/*
- * Copy a present and normal page if necessary.
+ * Copy a present and normal page.
*
- * NOTE! The usual case is that this doesn't need to do
- * anything, and can just return a positive value. That
- * will let the caller know that it can just increase
- * the page refcount and re-use the pte the traditional
- * way.
- *
- * But _if_ we need to copy it because it needs to be
- * pinned in the parent (and the child should get its own
- * copy rather than just a reference to the same page),
- * we'll do that here and return zero to let the caller
- * know we're done.
+ * NOTE! The usual case is that this isn't required;
+ * instead, the caller can just increase the page refcount
+ * and re-use the pte the traditional way.
*
* And if we need a pre-allocated page but don't yet have
* one, return a negative error to let the preallocation
@@ -884,25 +876,10 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
static inline int
copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
- struct page **prealloc, pte_t pte, struct page *page)
+ struct page **prealloc, struct page *page)
{
struct page *new_page;
-
- /*
- * What we want to do is to check whether this page may
- * have been pinned by the parent process. If so,
- * instead of wrprotect the pte on both sides, we copy
- * the page immediately so that we'll always guarantee
- * the pinned page won't be randomly replaced in the
- * future.
- *
- * The page pinning checks are just "has this mm ever
- * seen pinning", along with the (inexact) check of
- * the page count. That might give false positives for
- * for pinning, but it will work correctly.
- */
- if (likely(!page_needs_cow_for_dma(src_vma, page)))
- return 1;
+ pte_t pte;
new_page = *prealloc;
if (!new_page)
@@ -944,14 +921,16 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
struct page *page;
page = vm_normal_page(src_vma, addr, pte);
- if (page) {
- int retval;
-
- retval = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
- addr, rss, prealloc, pte, page);
- if (retval <= 0)
- return retval;
-
+ if (page && unlikely(page_needs_cow_for_dma(src_vma, page))) {
+ /*
+ * If this page may have been pinned by the parent process,
+ * copy the page immediately for the child so that we'll always
+ * guarantee the pinned page won't be randomly replaced in the
+ * future.
+ */
+ return copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
+ addr, rss, prealloc, page);
+ } else if (page) {
get_page(page);
page_dup_rmap(page, false);
rss[mm_counter(page)]++;
--
2.35.1
next prev parent reply other threads:[~2022-04-28 8:38 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-28 8:34 [PATCH v4 00/17] mm: COW fixes part 2: reliable GUP pins of anonymous pages David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 01/17] mm/rmap: fix missing swap_free() in try_to_unmap() after arch_unmap_one() failed David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 02/17] mm/hugetlb: take src_mm->write_protect_seq in copy_hugetlb_page_range() David Hildenbrand
2022-04-28 8:34 ` David Hildenbrand [this message]
2022-04-28 8:34 ` [PATCH v4 04/17] mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap() David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 05/17] mm/rmap: convert RMAP flags to a proper distinct rmap_t type David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 06/17] mm/rmap: remove do_page_add_anon_rmap() David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 07/17] mm/rmap: pass rmap flags to hugepage_add_anon_rmap() David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 08/17] mm/rmap: drop "compound" parameter from page_add_new_anon_rmap() David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 09/17] mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 10/17] mm/huge_memory: remove outdated VM_WARN_ON_ONCE_PAGE from unmap_page() David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 11/17] mm/page-flags: reuse PG_mappedtodisk as PG_anon_exclusive for PageAnon() pages David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 12/17] mm: remember exclusively mapped anonymous pages with PG_anon_exclusive David Hildenbrand
2022-04-29 18:26 ` Andrew Morton
2022-04-29 18:56 ` David Hildenbrand
2022-12-06 3:05 ` Miaohe Lin
2022-12-06 8:43 ` David Hildenbrand
2022-12-06 9:37 ` Miaohe Lin
2022-12-06 9:40 ` David Hildenbrand
2022-12-06 11:28 ` Miaohe Lin
2022-04-28 8:34 ` [PATCH v4 13/17] mm/rmap: fail try_to_migrate() early when setting a PMD migration entry fails David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 14/17] mm/gup: disallow follow_page(FOLL_PIN) David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 15/17] mm: support GUP-triggered unsharing of anonymous pages David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 16/17] mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page David Hildenbrand
2022-04-28 8:34 ` [PATCH v4 17/17] mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning David Hildenbrand
2022-04-28 8:37 ` [PATCH v4 00/17] mm: COW fixes part 2: reliable GUP pins of anonymous pages David Hildenbrand
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