Messages in this thread | | | Date | Mon, 18 Apr 2011 14:46:09 +0530 | From | Raghavendra D Prabhu <> | Subject | Re: [PATCH 1/1] Add check for dirty_writeback_interval in bdi_wakeup_thread_delayed |
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* On Mon, Apr 18, 2011 at 10:19:12AM +0300, Artem Bityutskiy <Artem.Bityutskiy@nokia.com> wrote: >On Sun, 2011-04-17 at 21:53 +0530, Raghavendra D Prabhu wrote: >> In the function bdi_wakeup_thread_delayed, no checks are performed on >> dirty_writeback_interval unlike other places and timeout is being set to >> zero as result, thus defeating the purpose. So, I have changed it to be >> passed default value of interval which is 500 centiseconds, when it is >> set to zero. >> I have also verified this and tested it.
>> Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net> > >If dirty_writeback_interval then the periodic write-back has to be >disabled. Which means we should rather do something like this: > >diff --git a/mm/backing-dev.c b/mm/backing-dev.c >index 0d9a036..f38722c 100644 >--- a/mm/backing-dev.c >+++ b/mm/backing-dev.c >@@ -334,10 +334,12 @@ static void wakeup_timer_fn(unsigned long data) > */ > void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) > { >- unsigned long timeout; >+ if (dirty_writeback_interval) { >+ unsigned long timeout; > >- timeout = msecs_to_jiffies(dirty_writeback_interval * 10); >- mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout); >+ timeout = msecs_to_jiffies(dirty_writeback_interval * 10); >+ mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout); >+ } > } > >I do not see why you use 500 centisecs instead - I think this is wrong. > >> --- >> mm/backing-dev.c | 5 ++++- >> 1 files changed, 4 insertions(+), 1 deletions(-)
>> diff --git a/mm/backing-dev.c b/mm/backing-dev.c >> index befc875..d06533c 100644 >> --- a/mm/backing-dev.c >> +++ b/mm/backing-dev.c >> @@ -336,7 +336,10 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) >> { >> unsigned long timeout;
>> - timeout = msecs_to_jiffies(dirty_writeback_interval * 10); >> + if (dirty_writeback_interval) >> + timeout = msecs_to_jiffies(dirty_writeback_interval * 10); >> + else >> + timeout = msecs_to_jiffies(5000); >> mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout); >> } Hi,
I have set it to 500 centisecs as that is the default value of dirty_writeback_interval. I used this logic for following reason: the purpose for which dirty_writeback_interval is set to 0 is to disable periodic writeback (http://tomoyo.sourceforge.jp/cgi-bin/lxr/source/fs/fs-writeback.c#L818) , whereas here (in bdi_wakeup_thread_delayed) it is being used for a different purpose -- to delay the bdi wakeup in order to reduce context switches for dirty inode writeback. Regarding the change you made: in that case won't it end up disabling the timer altogether ? which shouldn't happen given the original purpose of defining dirty_writeback_interval to zero. [unhandled content-type:application/pgp-signature] | |