Commit 5d42ab29 authored by Wei Yang's avatar Wei Yang Committed by Linus Torvalds
Browse files

mm/mmap.c: make vma_merge() comment more easy to understand 

Case 1/6, 2/7 and 3/8 have the same pattern and we handle them in the
same logic.

Rearrange the comment to make it a little easy for audience to
understand.

Link: http://lkml.kernel.org/r/20191030012445.16944-1-richardw.yang@linux.intel.com


Signed-off-by: default avatarWei Yang <richardw.yang@linux.intel.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Steve Capper <steve.capper@arm.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 35e3d566

mm/mmap.c

+12 −9
Original line number Diff line number Diff line
@@ -1091,15 +1091,18 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, 
 * the area passed down from mprotect_fixup, never extending beyond one

 * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:

 *

 *     AAAA             AAAA                AAAA          AAAA

 *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX

 *    cannot merge    might become    might become    might become

 *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or

 *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or

 *    mremap move:                                    PPPPXXXXXXXX 8

 *        AAAA

 *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN

 *    might become    case 1 below    case 2 below    case 3 below

 *     AAAA             AAAA                   AAAA

 *    PPPPPPNNNNNN    PPPPPPNNNNNN       PPPPPPNNNNNN

 *    cannot merge    might become       might become

 *                    PPNNNNNNNNNN       PPPPPPPPPPNN

 *    mmap, brk or    case 4 below       case 5 below

 *    mremap move:

 *                        AAAA               AAAA

 *                    PPPP    NNNN       PPPPNNNNXXXX

 *                    might become       might become

 *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or

 *                    PPPPPPPPNNNN 2 or  PPPPPPPPXXXX 7 or

 *                    PPPPNNNNNNNN 3     PPPPXXXXXXXX 8

 *

 * It is important for case 8 that the vma NNNN overlapping the

 * region AAAA is never going to extended over XXXX. Instead XXXX must

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