Commit 3ee48b6a authored by Cliff Wickman's avatar Cliff Wickman Committed by Ingo Molnar

mm, x86: Saving vmcore with non-lazy freeing of vmas

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: default avatarCliff Wickman <>
Cc: Andrew Morton <>
Cc: <>
LKML-Reference: <>
Signed-off-by: default avatarIngo Molnar <>
parent 37a2f9f3
......@@ -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__
......@@ -46,6 +46,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
} else
memcpy(buf, vaddr + offset, csize);
return csize;
......@@ -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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