Re: [PATCH v2 00/13] MADV_FREE support

[Daniel Micay]

On 05/12/15 06:10 AM, Pavel Machek wrote:
> On Wed 2015-11-04 10:25:54, Minchan Kim wrote:
>> MADV_FREE is on linux-next so long time. The reason was two, I think.
>>
>> 1. MADV_FREE code on reclaim path was really mess.
> 
> Could you explain what MADV_FREE does?
> 
> Comment in code says 'free the page only when there's memory
> pressure'. So I mark my caches MADV_FREE, no memory pressure, I can
> keep using it? And if there's memory pressure, what happens? I get
> zeros? SIGSEGV?

You get zeroes. It's not designed for that use case right now. It's for
malloc implementations to use internally. There would need to be a new
feature like MADV_FREE_UNDO for it to be usable for caches and it may
make more sense for that to be a separate feature entirely, i.e. have a
different flag for marking too (not sure) since it wouldn't need to
worry about whether stuff is touched.

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