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. Thanks. -- Best Regards Yan Zi
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