x86/mm: Add support for gbpages to kernel_ident_mapping_init() (66aad4fd) · Commits · 戴 / test

Kernel identity mappings on x86-64 kernels are created in two ways: by the early x86 boot code, or by kernel_ident_mapping_init(). Native kernels (which is the dominant usecase) use the former, but the kexec and the hibernation code uses kernel_ident_mapping_init(). There's a subtle difference between these two ways of how identity mappings are created, the current kernel_ident_mapping_init() code creates identity mappings always using 2MB page(PMD level) - while the native kernel boot path also utilizes gbpages where available. This difference is suboptimal both for performance and for memory usage: kernel_ident_mapping_init() needs to allocate pages for the page tables when creating the new identity mappings. This patch adds 1GB page(PUD level) support to kernel_ident_mapping_init() to address these concerns. The primary advantage would be better TLB coverage/performance, because we'd utilize 1GB TLBs instead of 2MB ones. It is also useful for machines with large number of memory to save paging structure allocations(around 4MB/TB using 2MB page) when setting identity mappings for all the memory, after using 1GB page it will consume only 8KB/TB. ( Note that this change alone does not activate gbpages in kexec, we are doing that in a separate patch. ) Signed-off-by:

Xunlei Pang <xlpang@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Young <dyoung@redhat.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Eric Biederman <ebiederm@xmission.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yinghai Lu <yinghai@kernel.org> Cc: akpm@linux-foundation.org Cc: kexec@lists.infradead.org Link: http://lkml.kernel.org/r/1493862171-8799-1-git-send-email-xlpang@redhat.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/boot/compressed/pagetable.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -70,7 +70,7 @@ static unsigned long level4p;
		* Due to relocation, pointers must be assigned at run time not build time.
		*/
		static struct x86_mapping_info mapping_info = {
		.pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
		.page_flag = __PAGE_KERNEL_LARGE_EXEC,
		};

		/* Locates and clears a region for a new top level page table. */

arch/x86/include/asm/init.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -4,8 +4,9 @@
		struct x86_mapping_info {
		void (alloc_pgt_page)(void ); / allocate buf for page table */
		void context; / context for alloc_pgt_page */
		unsigned long pmd_flag; /* page flag for PMD entry */
		unsigned long page_flag; /* page flag for PMD or PUD entry */
		unsigned long offset; /* ident mapping offset */
		bool direct_gbpages; /* PUD level 1GB page support */
		};

		int kernel_ident_mapping_init(struct x86_mapping_info info, pgd_t pgd_page,

arch/x86/kernel/machine_kexec_64.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -113,7 +113,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
		struct x86_mapping_info info = {
		.alloc_pgt_page = alloc_pgt_page,
		.context = image,
		.pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
		.page_flag = __PAGE_KERNEL_LARGE_EXEC,
		};
		unsigned long mstart, mend;
		pgd_t *level4p;

arch/x86/mm/ident_map.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -13,7 +13,7 @@ static void ident_pmd_init(struct x86_mapping_info info, pmd_t pmd_page,
		if (pmd_present(*pmd))
		continue;

		set_pmd(pmd, __pmd((addr - info->offset) \| info->pmd_flag));
		set_pmd(pmd, __pmd((addr - info->offset) \| info->page_flag));
		}
		}

		@@ -30,6 +30,18 @@ static int ident_pud_init(struct x86_mapping_info info, pud_t pud_page,
		if (next > end)
		next = end;

		if (info->direct_gbpages) {
		pud_t pudval;

		if (pud_present(*pud))
		continue;

		addr &= PUD_MASK;
		pudval = __pud((addr - info->offset) \| info->page_flag);
		set_pud(pud, pudval);
		continue;
		}

		if (pud_present(*pud)) {
		pmd = pmd_offset(pud, 0);
		ident_pmd_init(info, pmd, addr, next);

arch/x86/power/hibernate_64.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -104,7 +104,7 @@ static int set_up_temporary_mappings(void)
		{
		struct x86_mapping_info info = {
		.alloc_pgt_page = alloc_pgt_page,
		.pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
		.page_flag = __PAGE_KERNEL_LARGE_EXEC,
		.offset = __PAGE_OFFSET,
		};
		unsigned long mstart, mend;

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