Messages in this thread |  | | Date | Mon, 16 Dec 2019 14:34:26 +0200 | From | Ilias Apalodimas <> | Subject | Re: [PATCH][v2] page_pool: handle page recycle for NUMA_NO_NODE condition |
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Hi Michal, On Mon, Dec 16, 2019 at 01:15:57PM +0100, Michal Hocko wrote: > On Thu 12-12-19 09:34:14, Yunsheng Lin wrote: > > +CC Michal, Peter, Greg and Bjorn > > Because there has been disscusion about where and how the NUMA_NO_NODE > > should be handled before. > > I do not have a full context. What is the question here?
When we allocate pages for the page_pool API, during the init, the driver writer decides which NUMA node to use. The API can, in some cases recycle the memory, instead of freeing it and re-allocating it. If the NUMA node has changed (irq affinity for example), we forbid recycling and free the memory, since recycling and using memory on far NUMA nodes is more expensive (more expensive than recycling, at least on the architectures we tried anyway). Since this would be expensive to do it per packet, the burden falls on the driver writer for that. Drivers *have* to call page_pool_update_nid() or page_pool_nid_changed() if they want to check for that which runs once per NAPI cycle.
The current code in the API though does not account for NUMA_NO_NODE. That's what this is trying to fix. If the page_pool params are initialized with that, we *never* recycle the memory. This is happening because the API is allocating memory with 'nid = numa_mem_id()' if NUMA_NO_NODE is configured so the current if statement 'page_to_nid(page) == pool->p.nid' will never trigger.
The initial proposal was to check: pool->p.nid == NUMA_NO_NODE && page_to_nid(page) == numa_mem_id()));
After that the thread span out of control :) My question is do we *really* have to check for page_to_nid(page) == numa_mem_id()? if the architecture is not NUMA aware wouldn't pool->p.nid == NUMA_NO_NODE be enough?
Thanks /Ilias > -- > Michal Hocko > SUSE Labs
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