On Mon, Apr 10, 2017 at 12:49:40PM -0500, Zi Yan wrote: > On 10 Apr 2017, at 12:20, Mel Gorman wrote: > > > On Mon, Apr 10, 2017 at 11:45:08AM -0500, Zi Yan wrote: > >>> While this could be fixed with heavy locking, it's only necessary to > >>> make a copy of the PMD on the stack during change_pmd_range and avoid > >>> races. A new helper is created for this as the check if quite subtle and > >>> the > >>> existing similar helpful is not suitable. This passed 154 hours of testing > >>> (usually triggers between 20 minutes and 24 hours) without detecting bad > >>> PMDs or corruption. A basic test of an autonuma-intensive workload showed > >>> no significant change in behaviour. > >>> > >>> Signed-off-by: Mel Gorman <[email protected]> > >>> Cc: [email protected] > >> > >> Does this patch fix the same problem fixed by Kirill's patch here? > >> https://lkml.org/lkml/2017/3/2/347 > >> > > > > I don't think so. The race I'm concerned with is due to locks not being > > held and is in a different path. > > I do not agree. Kirill's patch is fixing the same race problem but in > zap_pmd_range(). > > The original autoNUMA code first clears PMD then sets it to protnone entry. > pmd_trans_huge() does not return TRUE because it saw cleared PMD, but > pmd_none_or_clear_bad() later saw the protnone entry and reported it as bad. > Is this the problem you are trying solve? > > Kirill's patch will pmdp_invalidate() the PMD entry, which keeps _PAGE_PSE > bit, > so pmd_trans_huge() will return TRUE. In this case, it also fixes > your race problem in change_pmd_range(). > > Let me know if I miss anything. >
Ok, now I see. I think you're correct and I withdraw the patch. -- Mel Gorman SUSE Labs
