mm, x86: Saving vmcore with non-lazy freeing of vmas (3ee48b6a) · Commits · 戴 / test

During the reading of /proc/vmcore the kernel is doing ioremap()/iounmap() repeatedly. And the buildup of un-flushed vm_area_struct's is causing a great deal of overhead. (rb_next() is chewing up most of that time). This solution is to provide function set_iounmap_nonlazy(). It causes a subsequent call to iounmap() to immediately purge the vma area (with try_purge_vmap_area_lazy()). With this patch we have seen the time for writing a 250MB compressed dump drop from 71 seconds to 44 seconds. Signed-off-by:

Cliff Wickman <cpw@sgi.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: kexec@lists.infradead.org Cc: <stable@kernel.org> LKML-Reference: <E1OwHZ4-0005WK-Tw@eag09.americas.sgi.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/io.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -206,6 +206,7 @@ static inline void __iomem *ioremap(resource_size_t offset, unsigned long size)

		extern void iounmap(volatile void __iomem *addr);

		extern void set_iounmap_nonlazy(void);

		#ifdef __KERNEL__

arch/x86/kernel/crash_dump_64.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -46,6 +46,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
		} else
		memcpy(buf, vaddr + offset, csize);

		set_iounmap_nonlazy();
		iounmap(vaddr);
		return csize;
		}

mm/vmalloc.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -516,6 +516,15 @@ static atomic_t vmap_lazy_nr = ATOMIC_INIT(0);
		/* for per-CPU blocks */
		static void purge_fragmented_blocks_allcpus(void);

		/*
		* called before a call to iounmap() if the caller wants vm_area_struct's
		* immediately freed.
		*/
		void set_iounmap_nonlazy(void)
		{
		atomic_set(&vmap_lazy_nr, lazy_max_pages()+1);
		}

		/*
		* Purges all lazily-freed vmap areas.
		*

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