Messages in this thread | | | Subject | Re: [v2 PATCH] move_pages.2: Returning positive value is a new error case | From | Yang Shi <> | Date | Thu, 30 Jan 2020 09:27:11 -0800 |
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On 1/30/20 5:48 AM, Michal Hocko wrote: > On Thu 30-01-20 13:56:20, Vlastimil Babka wrote: >> On 1/30/20 1:02 PM, Michal Hocko wrote: >>> On Thu 30-01-20 10:06:28, Vlastimil Babka wrote: >>>> On 1/29/20 10:48 PM, Yang Shi wrote: >>>>> Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), >>>>> the semantic of move_pages() has changed to return the number of >>>>> non-migrated pages if they were result of a non-fatal reasons (usually a >>>>> busy page). This was an unintentional change that hasn't been noticed >>>>> except for LTP tests which checked for the documented behavior. >>>>> >>>>> There are two ways to go around this change. We can even get back to the >>>>> original behavior and return -EAGAIN whenever migrate_pages is not able >>>> The manpage says EBUSY, not EAGAIN? And should its description be >>>> updated too? >>> The idea was that we _could_ return EAGAIN from the syscall if >>> migrate_pages > 0. >>> >>>> I.e. that it's no longer returned since 4.17? >>> I am pretty sure this will require a deeper consideration. Do we return >>> EIO/EINVAL? >> I thought the manpage says we return -EBUSY, but I misread it, this part >> was not about errno, but the status array. So there's nothing to update >> there, sorry about the noise. >> >> BTW, the suggestion to "Pre-initialization of the array to -1" means >> effectively it's pre-initialized to -EPERM. That's fine now as -EPERM is >> not one of the codes listed as possible to be returned via the array, >> but perhaps it's not entirely future-proof? > Hmm, I didn't realize EPERM is refering to 1. The wording however > suggests also any other value that cannot represent a valid NUMA node. > So maybe we should just drop the node about -1.
Or maybe we just say "any value which doesn't represent a valid NUMA node or valid error of status array"?
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