Re: [PATCH 05/14] vrange: Add new vrange(2) system call

H. Peter Anvin
2013-10-07T23:27:36Z

On 10/07/2013 04:14 PM, John Stultz wrote:
>>
>> I see from the change history of the patch that this was an madvise() at
>> some point, but was changed into a separate system call at some point,
>> does anyone remember why that was? A quick look through my LKML
>> archives doesn't really make it clear.
>
> The reason we can't use madvise, is that to properly handle error cases
> and report the pruge state, we need an extra argument.
>
> In much earlier versions, we just returned an error when setting
> NONVOLATILE if the data was purged. However, since we have to possibly
> do allocations when marking a range as non-volatile, we needed a way to
> properly handle that allocation failing. We can't just return ENOMEM, as
> we may have already marked purged memory as non-volatile.
>
> Thus, that's why with vrange, we return the number of bytes modified,
> along with the purge state. That way, if an error does occur we can
> return the purge state of the bytes successfully modified, and only
> return an error if nothing was changed, much like when a write fails.
>

I am not clear at all what the "purge state" is in this case.

-hpa