Messages in this thread |  | | | Date | Wed, 29 Apr 2009 11:40:44 +0200 | | From | Andrea Righi <> | | Subject | Re: [PATCH] mm: prevent divide error for small values of vm_dirty_bytes |
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On Wed, Apr 29, 2009 at 02:26:11AM -0700, David Rientjes wrote: > On Wed, 29 Apr 2009, 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(). > > > > Where exactly is the divide by 0 in get_dirty_limits()?
in the evaluation of the BDI's share ratio: ... if (bdi) { u64 bdi_dirty; long numerator, denominator; /* * Calculate this BDI's share of the dirty ratio. */ bdi_writeout_fraction(bdi, &numerator, &denominator); bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; bdi_dirty *= numerator; do_div(bdi_dirty, denominator); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ... More exactly: /home/righiandr/Software/linux/git/linux-2.6/mm/page-writeback.c:474 1186: 48 89 f0 mov %rsi,%rax 1189: 48 f7 f7 div %rdi
And looking at the trace:
[ 49.952195] RAX: 00000000000000c0 RBX: ffff88001de03b80 RCX: 28f5c28f5c28f5c3 [ 49.952195] RDX: 0000000000000000 RSI: 00000000000000c0 RDI: 0000000000000000 ^^^^^^^^^^^^^^^^^^^^^ > Is this because we forced the background threshold to be half of the dirty > threshold when its setting is greater?
No (see above).
-Andrea
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