linux-kernel - [PATCH] powerpc/mm: Fix growth direction for hugepages mmaps with slice

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Date:   Mon,  8 Jan 2018 15:39:19 +0100 (CET)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/mm: Fix growth direction for hugepages mmaps with
 slice

An application running with libhugetlbfs fails to allocate
additional pages to HEAP due to the hugemap being done
inconditionally as topdown mapping:

mmap(0x10080000, 1572864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0) = 0x73e80000
[...]
mmap(0x74000000, 1048576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d80000
munmap(0x73d80000, 1048576)             = 0
[...]
mmap(0x74000000, 1572864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d00000
munmap(0x73d00000, 1572864)             = 0
[...]
mmap(0x74000000, 1572864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d00000
munmap(0x73d00000, 1572864)             = 0
[...]

As one can see from the above strace log, mmap() allocates further
pages below the initial one.

This patch fixes it by taking into account MAP_GROWSDOWN flag.

Fixes: d0f13e3c20b6f ("[POWERPC] Introduce address space "slices" ")
Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/mm/hugetlbpage.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 5c5873259127..76330a976f9e 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -558,7 +558,8 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 		return radix__hugetlb_get_unmapped_area(file, addr, len,
 						       pgoff, flags);
 #endif
-	return slice_get_unmapped_area(addr, len, flags, mmu_psize, 1);
+	return slice_get_unmapped_area(addr, len, flags, mmu_psize,
+				       flags & MAP_GROWSDOWN);
 }
 #endif
 
-- 
2.13.3