Revision d7831a0bdf06b9f722b947bb0c205ff7d77cebd8 authored by Richard Kennedy on 30 June 2009, 18:41:35 UTC, committed by Linus Torvalds on 01 July 2009, 01:56:01 UTC
balance_dirty_pages can overreact and move all of the dirty pages to writeback unnecessarily. balance_dirty_pages makes its decision to throttle based on the number of dirty plus writeback pages that are over the calculated limit,so it will continue to move pages even when there are plenty of pages in writeback and less than the threshold still dirty. This allows it to overshoot its limits and move all the dirty pages to writeback while waiting for the drives to catch up and empty the writeback list. A simple fio test easily demonstrates this problem. fio --name=f1 --directory=/disk1 --size=2G -rw=write --name=f2 --directory=/disk2 --size=1G --rw=write --startdelay=10 This is the simplest fix I could find, but I'm not entirely sure that it alone will be enough for all cases. But it certainly is an improvement on my desktop machine writing to 2 disks. Do we need something more for machines with large arrays where bdi_threshold * number_of_drives is greater than the dirty_ratio ? Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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string_helpers.c
/*
* Helpers for formatting and printing strings
*
* Copyright 31 August 2008 James Bottomley
*/
#include <linux/kernel.h>
#include <linux/math64.h>
#include <linux/module.h>
#include <linux/string_helpers.h>
/**
* string_get_size - get the size in the specified units
* @size: The size to be converted
* @units: units to use (powers of 1000 or 1024)
* @buf: buffer to format to
* @len: length of buffer
*
* This function returns a string formatted to 3 significant figures
* giving the size in the required units. Returns 0 on success or
* error on failure. @buf is always zero terminated.
*
*/
int string_get_size(u64 size, const enum string_size_units units,
char *buf, int len)
{
const char *units_10[] = { "B", "kB", "MB", "GB", "TB", "PB",
"EB", "ZB", "YB", NULL};
const char *units_2[] = {"B", "KiB", "MiB", "GiB", "TiB", "PiB",
"EiB", "ZiB", "YiB", NULL };
const char **units_str[] = {
[STRING_UNITS_10] = units_10,
[STRING_UNITS_2] = units_2,
};
const unsigned int divisor[] = {
[STRING_UNITS_10] = 1000,
[STRING_UNITS_2] = 1024,
};
int i, j;
u64 remainder = 0, sf_cap;
char tmp[8];
tmp[0] = '\0';
i = 0;
if (size >= divisor[units]) {
while (size >= divisor[units] && units_str[units][i]) {
remainder = do_div(size, divisor[units]);
i++;
}
sf_cap = size;
for (j = 0; sf_cap*10 < 1000; j++)
sf_cap *= 10;
if (j) {
remainder *= 1000;
do_div(remainder, divisor[units]);
snprintf(tmp, sizeof(tmp), ".%03lld",
(unsigned long long)remainder);
tmp[j+1] = '\0';
}
}
snprintf(buf, len, "%lld%s %s", (unsigned long long)size,
tmp, units_str[units][i]);
return 0;
}
EXPORT_SYMBOL(string_get_size);
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