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Revision 7bf811a595a895b7a886dcf218d0d34f97df76dc authored by Josef Bacik on 08 October 2013, 02:11:09 UTC, committed by Chris Mason on 11 October 2013, 01:27:56 UTC 
Btrfs: limit delalloc pages outside of find_delalloc_range
 
Liu fixed part of this problem and unfortunately I steered him in slightly the
wrong direction and so didn't completely fix the problem.  The problem is we
limit the size of the delalloc range we are looking for to max bytes and then we
try to lock that range.  If we fail to lock the pages in that range we will
shrink the max bytes to a single page and re loop.  However if our first page is
inside of the delalloc range then we will end up limiting the end of the range
to a period before our first page.  This is illustrated below

[0 -------- delalloc range --------- 256mb]
                                  [page]

So find_delalloc_range will return with delalloc_start as 0 and end as 128mb,
and then we will notice that delalloc_start < *start and adjust it up, but not
adjust delalloc_end up, so things go sideways.  To fix this we need to not limit
the max bytes in find_delalloc_range, but in find_lock_delalloc_range and that
way we don't end up with this confusion.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
1 parent 4871c15
Raw File
mman.h 
#ifndef _LINUX_MMAN_H
#define _LINUX_MMAN_H

#include <linux/mm.h>
#include <linux/percpu_counter.h>

#include <linux/atomic.h>
#include <uapi/linux/mman.h>

extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
extern struct percpu_counter vm_committed_as;

#ifdef CONFIG_SMP
extern s32 vm_committed_as_batch;
#else
#define vm_committed_as_batch 0
#endif

unsigned long vm_memory_committed(void);

static inline void vm_acct_memory(long pages)
{
	__percpu_counter_add(&vm_committed_as, pages, vm_committed_as_batch);
}

static inline void vm_unacct_memory(long pages)
{
	vm_acct_memory(-pages);
}

/*
 * Allow architectures to handle additional protection bits
 */

#ifndef arch_calc_vm_prot_bits
#define arch_calc_vm_prot_bits(prot) 0
#endif

#ifndef arch_vm_get_page_prot
#define arch_vm_get_page_prot(vm_flags) __pgprot(0)
#endif

#ifndef arch_validate_prot
/*
 * This is called from mprotect().  PROT_GROWSDOWN and PROT_GROWSUP have
 * already been masked out.
 *
 * Returns true if the prot flags are valid
 */
static inline int arch_validate_prot(unsigned long prot)
{
	return (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM)) == 0;
}
#define arch_validate_prot arch_validate_prot
#endif

/*
 * Optimisation macro.  It is equivalent to:
 *      (x & bit1) ? bit2 : 0
 * but this version is faster.
 * ("bit1" and "bit2" must be single bits)
 */
#define _calc_vm_trans(x, bit1, bit2) \
  ((bit1) <= (bit2) ? ((x) & (bit1)) * ((bit2) / (bit1)) \
   : ((x) & (bit1)) / ((bit1) / (bit2)))

/*
 * Combine the mmap "prot" argument into "vm_flags" used internally.
 */
static inline unsigned long
calc_vm_prot_bits(unsigned long prot)
{
	return _calc_vm_trans(prot, PROT_READ,  VM_READ ) |
	       _calc_vm_trans(prot, PROT_WRITE, VM_WRITE) |
	       _calc_vm_trans(prot, PROT_EXEC,  VM_EXEC) |
	       arch_calc_vm_prot_bits(prot);
}

/*
 * Combine the mmap "flags" argument into "vm_flags" used internally.
 */
static inline unsigned long
calc_vm_flag_bits(unsigned long flags)
{
	return _calc_vm_trans(flags, MAP_GROWSDOWN,  VM_GROWSDOWN ) |
	       _calc_vm_trans(flags, MAP_DENYWRITE,  VM_DENYWRITE ) |
	       _calc_vm_trans(flags, MAP_LOCKED,     VM_LOCKED    );
}
#endif /* _LINUX_MMAN_H */
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