ksm: no debug in page_dup_rmap() (21333b2b) · Commits · 戴 / test

page_dup_rmap(), used on each mapped page when forking, was originally just an inline atomic_inc of mapcount. 2.6.22 added CONFIG_DEBUG_VM out-of-line checks to it, which would need to be ever-so-slightly complicated to allow for the PageKsm() we're about to define. But I think these checks never caught anything. And if it's coding errors we're worried about, such checks should be in page_remove_rmap() too, not just when forking; whereas if it's pagetable corruption we're worried about, then they shouldn't be limited to CONFIG_DEBUG_VM. Oh, just revert page_dup_rmap() to an inline atomic_inc of mapcount. Signed-off-by:

Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by:

Chris Wright <chrisw@redhat.com> Signed-off-by:

Izik Eidus <ieidus@redhat.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Avi Kivity <avi@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/rmap.h

+1 −5

Original line number	Diff line number	Diff line
		@@ -71,14 +71,10 @@ void page_add_new_anon_rmap(struct page , struct vm_area_struct , unsigned lon
		void page_add_file_rmap(struct page *);
		void page_remove_rmap(struct page *);

		#ifdef CONFIG_DEBUG_VM
		void page_dup_rmap(struct page page, struct vm_area_struct vma, unsigned long address);
		#else
		static inline void page_dup_rmap(struct page page, struct vm_area_struct vma, unsigned long address)
		static inline void page_dup_rmap(struct page *page)
		{
		atomic_inc(&page->_mapcount);
		}
		#endif

		/*
		* Called from mm/vmscan.c to handle paging out

mm/memory.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -597,7 +597,7 @@ copy_one_pte(struct mm_struct dst_mm, struct mm_struct src_mm,
		page = vm_normal_page(vma, addr, pte);
		if (page) {
		get_page(page);
		page_dup_rmap(page, vma, addr);
		page_dup_rmap(page);
		rss[!!PageAnon(page)]++;
		}

mm/rmap.c

+0 −21

Original line number	Diff line number	Diff line
		@@ -710,27 +710,6 @@ void page_add_file_rmap(struct page *page)
		}
		}

		#ifdef CONFIG_DEBUG_VM
		/**
		* page_dup_rmap - duplicate pte mapping to a page
		* @page: the page to add the mapping to
		* @vma: the vm area being duplicated
		* @address: the user virtual address mapped
		*
		* For copy_page_range only: minimal extract from page_add_file_rmap /
		* page_add_anon_rmap, avoiding unnecessary tests (already checked) so it's
		* quicker.
		*
		* The caller needs to hold the pte lock.
		*/
		void page_dup_rmap(struct page page, struct vm_area_struct vma, unsigned long address)
		{
		if (PageAnon(page))
		__page_check_anon_rmap(page, vma, address);
		atomic_inc(&page->_mapcount);
		}
		#endif

		/**
		* page_remove_rmap - take down pte mapping from a page
		* @page: page to remove mapping from

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