On Fri, 11 Jul 2014 12:18:27 +0400 Maxim Patlasov <[email protected]> wrote:
> Under memory pressure, it is possible for dirty_thresh, calculated by > global_dirty_limits() in balance_dirty_pages(), to equal zero. Under what circumstances? Really small values of vm_dirty_bytes? > Then, if > strictlimit is true, bdi_dirty_limits() tries to resolve the proportion: > > bdi_bg_thresh : bdi_thresh = background_thresh : dirty_thresh > > by dividing by zero. > > ... > > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -1306,9 +1306,9 @@ static inline void bdi_dirty_limits(struct > backing_dev_info *bdi, > *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); > > if (bdi_bg_thresh) > - *bdi_bg_thresh = div_u64((u64)*bdi_thresh * > - background_thresh, > - dirty_thresh); > + *bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh * > + background_thresh, > + dirty_thresh) : 0; This introduces a peculiar discontinuity: if dirty_thresh==3, treat it as 3 if dirty_thresh==2, treat it as 2 if dirty_thresh==1, treat it as 1 if dirty_thresh==0, treat it as infinity Would it not make more sense to change global_dirty_limits() to convert 0 to 1? With an appropriate comment, obviously. Or maybe the fix lies elsewhere. Please do tell us how this zero comes about. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
