linux-kernel - [RFC PATCH 3/3] EXPERIMENTAL: x86/module: use __GFP_UNMAPPED in module

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Message-Id: <20220127085608.306306-4-rppt@kernel.org>
Date:   Thu, 27 Jan 2022 10:56:08 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Mike Rapoport <rppt@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: [RFC PATCH 3/3] EXPERIMENTAL: x86/module: use __GFP_UNMAPPED in module_alloc

From: Mike Rapoport <rppt@...ux.ibm.com>

The permissions of pages allocated by module_alloc() are frequently updated
using set_memory and set_direct_map APIs. Such permission changes cause
fragmentation of the direct map.

Since module_alloc() essentially wraps vmalloc(), the memory allocated by it
is mapped in the vmalloc area and it can be completely removed from the
direct map.

Use __GFP_UNMAPPED to utilize caching of unmapped pages done by the page
allocator.

Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
---
 arch/x86/kernel/module.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 95fa745e310a..70aa6ec0cc16 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -75,7 +75,7 @@ void *module_alloc(unsigned long size)
 
 	p = __vmalloc_node_range(size, MODULE_ALIGN,
 				    MODULES_VADDR + get_module_load_offset(),
-				    MODULES_END, gfp_mask,
+				    MODULES_END, gfp_mask | __GFP_UNMAPPED,
 				    PAGE_KERNEL, VM_DEFER_KMEMLEAK, NUMA_NO_NODE,
 				    __builtin_return_address(0));
 	if (p && (kasan_module_alloc(p, size, gfp_mask) < 0)) {
-- 
2.34.1