Messages in this thread | | | Date | Wed, 29 Apr 2009 13:02:27 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [PATCH] mm: prevent divide error for small values of vm_dirty_bytes |
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On Wed, 29 Apr 2009, Andrea Righi wrote:
> On Wed, Apr 29, 2009 at 10:44:36AM +0200, Peter Zijlstra wrote: > > On Wed, 2009-04-29 at 10:29 +0200, Andrea Righi wrote: > > > Avoid to set less than two pages for vm_dirty_byte: this is necessary to avoid > > > potential division by 0 (like the following) in get_dirty_limits(). > > > > isn't changing the .extra1 in the sysctl table a better fix? > > I thought about that and probably you're right. But, in the first case > if the user writes a value < 2*PAGE_SIZE vm_dirty_bytes is explicitly > set to 2*PAGE_SIZE. In the other case the value is just ignored. > > Maybe the second case could generate some unexpected behaviours for > the user. For example, the user writes X < 2*PAGE_SIZE to > /proc/sys/vm/dirty_bytes, and could think that the system has started to > use this new configuration, but it isn't actually. > > So, probably the best way is to change .extra1 and add a note in the > documentation (see below). >
This is only caused by bdi, not by the dirty ratio itself; shouldn't the appropriate fix be in calc_period_shift()? In other words, allow dirty thresholds to be less than 2 * PAGE_SIZE but prevent the bdi fraction from having a zero denominator?
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