Re: [PATCH v3 01/17] mm: support madvise(MADV_FREE)

[Daniel Micay]

On 13/11/15 01:15 AM, Minchan Kim wrote:
> On Thu, Nov 12, 2015 at 12:21:30AM -0500, Daniel Micay wrote:
>>> I also think that the kernel should commit to either zeroing the page
>>> or leaving it unchanged in response to MADV_FREE (even if the decision
>>> of which to do is made later on).  I think that your patch series does
>>> this, but only after a few of the patches are applied (the swap entry
>>> freeing), and I think that it should be a real guaranteed part of the
>>> semantics and maybe have a test case.
>>
>> This would be a good thing to test because it would be required to add
>> MADV_FREE_UNDO down the road. It would mean the same semantics as the
>> MEM_RESET and MEM_RESET_UNDO features on Windows, and there's probably
>> value in that for the sake of migrating existing software too.
> 
> So, do you mean that we could implement MADV_FREE_UNDO with "read"
> opearation("just access bit marking) easily in future?
> 
> If so, it would be good reason to change MADV_FREE from dirty bit to
> access bit. Okay, I will look at that.

I just meant testing that the data is either zero or the old data if
it's read before it's written to. Not having it stay around once there
is a read. Not sure if that's what Andy meant.

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