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Subject[15/82] mm, x86: Saving vmcore with non-lazy freeing of vmas
2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Cliff Wickman <cpw@sgi.com>

commit 3ee48b6af49cf534ca2f481ecc484b156a41451d upstream.

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
LKML-Reference: <E1OwHZ4-0005WK-Tw@eag09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/include/asm/io.h | 1 +
arch/x86/kernel/crash_dump_64.c | 1 +
mm/vmalloc.c | 9 +++++++++
3 files changed, 11 insertions(+)

--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -206,6 +206,7 @@ static inline void __iomem *ioremap(reso

extern void iounmap(volatile void __iomem *addr);

+extern void set_iounmap_nonlazy(void);

#ifdef __KERNEL__

--- a/arch/x86/kernel/crash_dump_64.c
+++ b/arch/x86/kernel/crash_dump_64.c
@@ -46,6 +46,7 @@ ssize_t copy_oldmem_page(unsigned long p
} else
memcpy(buf, vaddr + offset, csize);

+ set_iounmap_nonlazy();
iounmap(vaddr);
return csize;
}
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -513,6 +513,15 @@ static atomic_t vmap_lazy_nr = ATOMIC_IN
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.
*
* If sync is 0 then don't purge if there is already a purge in progress.



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