linux-kernel - [16/66] mm, x86: Saving vmcore with non-lazy freeing of vmas

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Message-Id: <20101119220123.488019055@clark.site>
Date:	Fri, 19 Nov 2010 14:00:47 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Cliff Wickman <cpw@....com>, kexec@...ts.infradead.org,
	Ingo Molnar <mingo@...e.hu>
Subject: [16/66] mm, x86: Saving vmcore with non-lazy freeing of vmas

2.6.36-stable review patch.  If anyone has any objections, please let us know.

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

From: Cliff Wickman <cpw@....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@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: kexec@...ts.infradead.org
LKML-Reference: <E1OwHZ4-0005WK-Tw@...09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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
@@ -517,6 +517,15 @@ 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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