linux-kernel - [PATCH v3 5/5] powerpc/mm: Fix growth direction for hugepages mmaps with slice

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Date:   Wed, 24 Jan 2018 10:02:34 +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>, aneesh.kumar@...ux.vnet.ibm.com
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v3 5/5] 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 because no space is available on top of it.

This patch fixes it by requesting bottomup mapping as the non
generic hugetlb_get_unmapped_area() does

Fixes: d0f13e3c20b6f ("[POWERPC] Introduce address space "slices" ")
Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 v3: Was a standalone patch before, but conflicts with this serie.

 arch/powerpc/mm/hugetlbpage.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 79e1378ee303..368ea6b248ad 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -558,7 +558,7 @@ 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, 0);
 }
 #endif
 
-- 
2.13.3