The estimation value will start from 100MB/s and adapt to the real bandwidth in seconds. It's pretty accurate for common filesystems. As the first use case, it replaces the static 100MB/s value used for 'bw' calculation in balance_dirty_pages(). The overheads won't be high because the bdi bandwidth udpate only occurs in >10ms intervals. Initially it's only estimated in balance_dirty_pages() because this is the most reliable place to get reasonable large bandwidth -- the bdi is normally fully utilized when bdi_thresh is reached. Then Shaohua recommends to also do it in the flusher thread, to keep the value updated when there are only periodic/background writeback and no tasks throttled. The estimation cannot be done purely in the flusher thread because it's not sufficient for NFS. NFS writeback won't block at get_request_wait(), so tend to complete quickly. Another problem is, slow devices may take dozens of seconds to write the initial 64MB chunk (write_bandwidth starts with 100MB/s, this translates to 64MB nr_to_write). So it may take more than 1 minute to adapt to the smallish bandwidth if the bandwidth is only updated in the flusher thread. CC: Li Shaohua Signed-off-by: Wu Fengguang --- fs/fs-writeback.c | 4 ++++ include/linux/backing-dev.h | 1 + include/linux/writeback.h | 3 +++ mm/backing-dev.c | 1 + mm/page-writeback.c | 33 ++++++++++++++++++++++++++++++++- 5 files changed, 41 insertions(+), 1 deletion(-) --- linux-next.orig/include/linux/backing-dev.h 2010-09-09 16:02:43.000000000 +0800 +++ linux-next/include/linux/backing-dev.h 2010-09-09 16:02:45.000000000 +0800 @@ -76,6 +76,7 @@ struct backing_dev_info { struct prop_local_percpu completions; int dirty_exceeded; + int write_bandwidth; unsigned int min_ratio; unsigned int max_ratio, max_prop_frac; --- linux-next.orig/mm/backing-dev.c 2010-09-09 16:02:43.000000000 +0800 +++ linux-next/mm/backing-dev.c 2010-09-09 16:02:45.000000000 +0800 @@ -658,6 +658,7 @@ int bdi_init(struct backing_dev_info *bd goto err; } + bdi->write_bandwidth = 100 << 20; bdi->dirty_exceeded = 0; err = prop_local_init_percpu(&bdi->completions); --- linux-next.orig/fs/fs-writeback.c 2010-09-09 14:13:21.000000000 +0800 +++ linux-next/fs/fs-writeback.c 2010-09-09 16:02:46.000000000 +0800 @@ -603,6 +603,8 @@ static long wb_writeback(struct bdi_writ .range_cyclic = work->range_cyclic, }; unsigned long oldest_jif; + unsigned long bw_time; + s64 bw_written = 0; long wrote = 0; struct inode *inode; @@ -616,6 +618,7 @@ static long wb_writeback(struct bdi_writ wbc.range_end = LLONG_MAX; } + bdi_update_write_bandwidth(wb->bdi, &bw_time, &bw_written); wbc.wb_start = jiffies; /* livelock avoidance */ for (;;) { /* @@ -641,6 +644,7 @@ static long wb_writeback(struct bdi_writ else writeback_inodes_wb(wb, &wbc); trace_wbc_writeback_written(&wbc, wb->bdi); + bdi_update_write_bandwidth(wb->bdi, &bw_time, &bw_written); work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write; --- linux-next.orig/mm/page-writeback.c 2010-09-09 16:02:43.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-09-09 16:04:23.000000000 +0800 @@ -449,6 +449,32 @@ unsigned long bdi_dirty_limit(struct bac return bdi_dirty; } +void bdi_update_write_bandwidth(struct backing_dev_info *bdi, + unsigned long *bw_time, + s64 *bw_written) +{ + unsigned long pages; + unsigned long time; + unsigned long bw; + unsigned long w; + + if (*bw_written == 0) + goto start_over; + + time = jiffies - *bw_time; + if (time < HZ/100) + return; + + pages = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]) - *bw_written; + bw = HZ * PAGE_CACHE_SIZE * pages / time; + w = clamp_t(unsigned long, time / (HZ/100), 1, 128); + + bdi->write_bandwidth = (bdi->write_bandwidth * (1024-w) + bw * w) >> 10; +start_over: + *bw_written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); + *bw_time = jiffies; +} + /* * balance_dirty_pages() must be called by processes which are generating dirty * data. It looks at the number of dirty pages in the machine and will force @@ -471,6 +497,8 @@ static void balance_dirty_pages(struct a bool dirty_exceeded = false; struct backing_dev_info *bdi = mapping->backing_dev_info; long numerator, denominator; + unsigned long bw_time; + s64 bw_written = 0; for (;;) { /* @@ -536,10 +564,12 @@ static void balance_dirty_pages(struct a bdi_thresh - bdi_thresh / DIRTY_SOFT_THROTTLE_RATIO) goto check_exceeded; + bdi_update_write_bandwidth(bdi, &bw_time, &bw_written); + gap = bdi_thresh > (bdi_nr_reclaimable + bdi_nr_writeback) ? bdi_thresh - (bdi_nr_reclaimable + bdi_nr_writeback) : 0; - bw = (100 << 20) * gap / + bw = bdi->write_bandwidth * gap / (bdi_thresh / DIRTY_SOFT_THROTTLE_RATIO + 1); pause = HZ * (pages_dirtied << PAGE_CACHE_SHIFT) / (bw + 1); @@ -562,6 +592,7 @@ static void balance_dirty_pages(struct a if (signal_pending(current)) break; + bdi_update_write_bandwidth(bdi, &bw_time, &bw_written); check_exceeded: /* * The bdi thresh is somehow "soft" limit derived from the --- linux-next.orig/include/linux/writeback.h 2010-09-09 15:51:38.000000000 +0800 +++ linux-next/include/linux/writeback.h 2010-09-09 16:02:46.000000000 +0800 @@ -136,6 +136,9 @@ int dirty_writeback_centisecs_handler(st void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty); unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty); +void bdi_update_write_bandwidth(struct backing_dev_info *bdi, + unsigned long *bw_time, + s64 *bw_written); void page_writeback_init(void); void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/