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authorRick Edgecombe <rick.p.edgecombe@intel.com>2024-03-26 05:16:44 +0300
committerAndrew Morton <akpm@linux-foundation.org>2024-04-26 06:56:25 +0300
commit529ce23a764f25d172198b4c6ba90f1e2ad17f93 (patch)
tree7a3c033c5c09cfc0c2345134291e059afa66d47f /drivers/char
parent5def1e0f476da713141269d86815aba7c2817cb5 (diff)
downloadlinux-529ce23a764f25d172198b4c6ba90f1e2ad17f93.tar.xz
mm: switch mm->get_unmapped_area() to a flag
The mm_struct contains a function pointer *get_unmapped_area(), which is set to either arch_get_unmapped_area() or arch_get_unmapped_area_topdown() during the initialization of the mm. Since the function pointer only ever points to two functions that are named the same across all arch's, a function pointer is not really required. In addition future changes will want to add versions of the functions that take additional arguments. So to save a pointers worth of bytes in mm_struct, and prevent adding additional function pointers to mm_struct in future changes, remove it and keep the information about which get_unmapped_area() to use in a flag. Add the new flag to MMF_INIT_MASK so it doesn't get clobbered on fork by mmf_init_flags(). Most MM flags get clobbered on fork. In the pre-existing behavior mm->get_unmapped_area() would get copied to the new mm in dup_mm(), so not clobbering the flag preserves the existing behavior around inheriting the topdown-ness. Introduce a helper, mm_get_unmapped_area(), to easily convert code that refers to the old function pointer to instead select and call either arch_get_unmapped_area() or arch_get_unmapped_area_topdown() based on the flag. Then drop the mm->get_unmapped_area() function pointer. Leave the get_unmapped_area() pointer in struct file_operations alone. The main purpose of this change is to reorganize in preparation for future changes, but it also converts the calls of mm->get_unmapped_area() from indirect branches into a direct ones. The stress-ng bigheap benchmark calls realloc a lot, which calls through get_unmapped_area() in the kernel. On x86, the change yielded a ~1% improvement there on a retpoline config. In testing a few x86 configs, removing the pointer unfortunately didn't result in any actual size reductions in the compiled layout of mm_struct. But depending on compiler or arch alignment requirements, the change could shrink the size of mm_struct. Link: https://lkml.kernel.org/r/20240326021656.202649-3-rick.p.edgecombe@intel.com Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org> Cc: Borislav Petkov (AMD) <bp@alien8.de> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Deepak Gupta <debug@rivosinc.com> Cc: Guo Ren <guoren@kernel.org> Cc: Helge Deller <deller@gmx.de> Cc: H. Peter Anvin (Intel) <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Kees Cook <keescook@chromium.org> Cc: Mark Brown <broonie@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'drivers/char')
-rw-r--r--drivers/char/mem.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 3c6670cf905f..9b80e622ae80 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -544,7 +544,7 @@ static unsigned long get_unmapped_area_zero(struct file *file,
}
/* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
- return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
+ return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags);
#else
return -ENOSYS;
#endif