Commit 195cf453 authored by Bron Gondwana's avatar Bron Gondwana Committed by Linus Torvalds
Browse files

mm/page-writeback: highmem_is_dirtyable option 



Add vm.highmem_is_dirtyable toggle

A 32 bit machine with HIGHMEM64 enabled running DCC has an MMAPed file of
approximately 2Gb size which contains a hash format that is written
randomly by the dbclean process.  On 2.6.16 this process took a few
minutes.  With lowmem only accounting of dirty ratios, this takes about 12
hours of 100% disk IO, all random writes.

Include a toggle in /proc/sys/vm/highmem_is_dirtyable which can be set to 1 to
add the highmem back to the total available memory count.

[akpm@linux-foundation.org: Fix the CONFIG_DETECT_SOFTLOCKUP=y build]
Signed-off-by: default avatarBron Gondwana <brong@fastmail.fm>
Cc: Ethan Solomita <solo@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: WU Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3dfa5721

Documentation/filesystems/proc.txt

+15 −0
Original line number Diff line number Diff line
@@ -1315,6 +1315,21 @@ for writeout by the pdflush daemons. It is expressed in 100'ths of a second. 
Data which has been dirty in-memory for longer than this interval will be

written out next time a pdflush daemon wakes up.



highmem_is_dirtyable

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



Only present if CONFIG_HIGHMEM is set.



This defaults to 0 (false), meaning that the ratios set above are calculated

as a percentage of lowmem only.  This protects against excessive scanning

in page reclaim, swapping and general VM distress.



Setting this to 1 can be useful on 32 bit machines where you want to make

random changes within an MMAPed file that is larger than your available

lowmem without causing large quantities of random IO.  Is is safe if the

behavior of all programs running on the machine is known and memory will

not be otherwise stressed.



legacy_va_layout

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

Documentation/sysctl/vm.txt

+4 −3
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ Currently, these files are in /proc/sys/vm: 
- dirty_background_ratio

- dirty_expire_centisecs

- dirty_writeback_centisecs

- highmem_is_dirtyable   (only if CONFIG_HIGHMEM set)

- max_map_count

- min_free_kbytes

- laptop_mode
@@ -40,9 +41,9 @@ Currently, these files are in /proc/sys/vm: 
==============================================================



dirty_ratio, dirty_background_ratio, dirty_expire_centisecs,

dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode,

block_dump, swap_token_timeout, drop-caches,

hugepages_treat_as_movable:

dirty_writeback_centisecs, highmem_is_dirtyable,

vfs_cache_pressure, laptop_mode, block_dump, swap_token_timeout,

drop-caches, hugepages_treat_as_movable:



See Documentation/filesystems/proc.txt

include/linux/writeback.h

+1 −0
Original line number Diff line number Diff line
@@ -100,6 +100,7 @@ extern int dirty_background_ratio; 
extern int vm_dirty_ratio;

extern int dirty_writeback_interval;

extern int dirty_expire_interval;

extern int vm_highmem_is_dirtyable;

extern int block_dump;

extern int laptop_mode;

kernel/sysctl.c

+17 −1
Original line number Diff line number Diff line
@@ -84,8 +84,11 @@ extern int sysctl_stat_interval; 
extern int latencytop_enabled;



/* Constants used for minimum and  maximum */

#ifdef CONFIG_DETECT_SOFTLOCKUP

#if defined(CONFIG_DETECT_SOFTLOCKUP) || defined(CONFIG_HIGHMEM)

static int one = 1;

#endif



#ifdef CONFIG_DETECT_SOFTLOCKUP

static int sixty = 60;

#endif
@@ -1150,6 +1153,19 @@ static struct ctl_table vm_table[] = { 
		.extra1		= &zero,

	},

#endif

#ifdef CONFIG_HIGHMEM

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "highmem_is_dirtyable",

		.data		= &vm_highmem_is_dirtyable,

		.maxlen		= sizeof(vm_highmem_is_dirtyable),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec_minmax,

		.strategy	= &sysctl_intvec,

		.extra1		= &zero,

		.extra2		= &one,

	},

#endif

/*

 * NOTE: do not add new entries to this table unless you have read

 * Documentation/sysctl/ctl_unnumbered.txt

mm/page-writeback.c

+10 −1
Original line number Diff line number Diff line
@@ -68,6 +68,12 @@ static inline long sync_writeback_pages(void) 
 */

int dirty_background_ratio = 5;



/*

 * free highmem will not be subtracted from the total free memory

 * for calculating free ratios if vm_highmem_is_dirtyable is true

 */

int vm_highmem_is_dirtyable;



/*

 * The generator of dirty data starts writeback at this percentage

 */
@@ -287,7 +293,10 @@ static unsigned long determine_dirtyable_memory(void) 
	x = global_page_state(NR_FREE_PAGES)

		+ global_page_state(NR_INACTIVE)

		+ global_page_state(NR_ACTIVE);



	if (!vm_highmem_is_dirtyable)

		x -= highmem_dirtyable_memory(x);



	return x + 1;	/* Ensure that we never return 0 */

}

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