MAX_WRITEBACK_PAGES was hard-coded to 1024 because of a concern of not holding I_SYNC for too long. But this shouldn't be a concern since I_LOCK and I_SYNC have been separated. So make it be a tunable and change the default to be 32768. This change is helpful for ext4 since it means we write out large file in bigger chunks than just 4 megabytes at a time, so that when we have multiple large files in the page cache waiting for writeback, the files don't end up getting interleaved. There shouldn't be any downside. http://bugzilla.kernel.org/show_bug.cgi?id=13930 Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx> --- include/linux/writeback.h | 1 + kernel/sysctl.c | 8 ++++++++ mm/page-writeback.c | 27 ++++++++++++++------------- 3 files changed, 23 insertions(+), 13 deletions(-) diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 3224820..c1e6c08 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -110,6 +110,7 @@ extern int vm_dirty_ratio; extern unsigned long vm_dirty_bytes; extern unsigned int dirty_writeback_interval; extern unsigned int dirty_expire_interval; +extern unsigned int max_writeback_pages; extern int vm_highmem_is_dirtyable; extern int block_dump; extern int laptop_mode; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 58be760..06d1c4c 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1104,6 +1104,14 @@ static struct ctl_table vm_table[] = { .proc_handler = &proc_dointvec, }, { + .ctl_name = CTL_UNNUMBERED, + .procname = "max_writeback_pages", + .data = &max_writeback_pages, + .maxlen = sizeof(max_writeback_pages), + .mode = 0644, + .proc_handler = &proc_dointvec, + }, + { .ctl_name = VM_NR_PDFLUSH_THREADS, .procname = "nr_pdflush_threads", .data = &nr_pdflush_threads, diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 81627eb..eac8026 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -36,15 +36,6 @@ #include <linux/pagevec.h> /* - * The maximum number of pages to writeout in a single bdflush/kupdate - * operation. We do this so we don't hold I_SYNC against an inode for - * enormous amounts of time, which would block a userspace task which has - * been forced to throttle against that inode. Also, the code reevaluates - * the dirty each time it has written this many pages. - */ -#define MAX_WRITEBACK_PAGES 1024 - -/* * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited * will look to see if it needs to force writeback or throttling. */ @@ -64,6 +55,16 @@ static inline long sync_writeback_pages(void) /* The following parameters are exported via /proc/sys/vm */ /* + * The maximum number of pages to writeout in a single bdflush/kupdate + * operation. We used to limit this to 1024 pages to avoid holding + * I_SYNC against an inode for a long period of times, but since + * I_SYNC has been separated out from I_LOCK, the only time a process + * waits for I_SYNC is when it is calling fsync() or otherwise forcing + * out the inode. + */ +unsigned int max_writeback_pages = 32768; + +/* * Start background writeback (via pdflush) at this percentage */ int dirty_background_ratio = 10; @@ -708,10 +709,10 @@ static void background_writeout(unsigned long _min_pages) break; wbc.more_io = 0; wbc.encountered_congestion = 0; - wbc.nr_to_write = MAX_WRITEBACK_PAGES; + wbc.nr_to_write = max_writeback_pages; wbc.pages_skipped = 0; writeback_inodes(&wbc); - min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; + min_pages -= max_writeback_pages - wbc.nr_to_write; if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { /* Wrote less than expected */ if (wbc.encountered_congestion || wbc.more_io) @@ -783,7 +784,7 @@ static void wb_kupdate(unsigned long arg) while (nr_to_write > 0) { wbc.more_io = 0; wbc.encountered_congestion = 0; - wbc.nr_to_write = MAX_WRITEBACK_PAGES; + wbc.nr_to_write = max_writeback_pages; writeback_inodes(&wbc); if (wbc.nr_to_write > 0) { if (wbc.encountered_congestion || wbc.more_io) @@ -791,7 +792,7 @@ static void wb_kupdate(unsigned long arg) else break; /* All the old data is written */ } - nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; + nr_to_write -= max_writeback_pages - wbc.nr_to_write; } if (time_before(next_jif, jiffies + HZ)) next_jif = jiffies + HZ; -- 1.6.3.2.1.gb9f7d.dirty -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
