Shared memory mappings for devices [LWN.net]

Shared memory mappings for devices

Posted May 7, 2018 20:31 UTC (Mon) by willy (subscriber, #9762)
Parent article: Shared memory mappings for devices

Argh, I missed this session. Thanks for writing this up, Jake!

I have a preliminary patch to use an IDR to assign each mm_struct a u32 ID. There are various details around how quickly those can be reused. It actually saves memory (replacing the list_head with a u32). I'll try to get that finished up soon.

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Shared memory mappings for devices

Posted May 7, 2018 20:42 UTC (Mon) by luto (subscriber, #39314) [Link] (2 responses)

On x86, we already have ctx_id. That could easily be moved to core code.

Shared memory mappings for devices

Posted May 7, 2018 21:02 UTC (Mon) by willy (subscriber, #9762) [Link] (1 responses)

I talked with Dave Hansen about ctx_id already. mm_id can replace it.

Shared memory mappings for devices

Posted May 7, 2018 21:37 UTC (Mon) by luto (subscriber, #39314) [Link]

Would it be u64? It’s quite important that it never gets reused.

Shared memory mappings for devices

Posted May 8, 2018 21:29 UTC (Tue) by mirabilos (subscriber, #84359) [Link] (6 responses)

What’s an IDR?

Asking for my acronyms database…

Shared memory mappings for devices

Posted May 8, 2018 21:33 UTC (Tue) by willy (subscriber, #9762) [Link] (3 responses)

https://www.kernel.org/doc/html/latest/core-api/idr.html

Shared memory mappings for devices

Posted May 11, 2018 7:37 UTC (Fri) by jem (subscriber, #24231) [Link] (2 responses)

Ironically, the documentation you linked to doesn't explain either what IDR or IDA are short for.

I miss Byte magazine, which meticulously spelled out an acronym the first time it appeared in an article, no matter how common. For example: "Random Access Memory (RAM)".

Shared memory mappings for devices

Posted May 11, 2018 14:16 UTC (Fri) by willy (subscriber, #9762) [Link]

Oh, I have no idea what either IDR or IDA stand for. It's not stated anywhere in the source code. I suppose I could search the mailing lists to find if there was any explanation when they were first published.

Shared memory mappings for devices

Posted May 15, 2018 23:52 UTC (Tue) by giraffedata (guest, #1954) [Link]

IBM used to do that in all its manuals as well, and it's an irritating style because acronyms are not abbreviations - they're words in their own right that are better known and have more meaning than the words from which they are derived. Sometimes the acquired meanings even contradict those words. The etymology of the acronym is still useful, of course, but the right way to do it is RAM (Random Access Memory), not Random Access Memory (RAM).

RAM is an interesting example, by the way, because words used illogically was another peeve Byte editors had and the magazine never used RAM to mean what most people meant by it: read/write memory. The term in Byte for that was "programmable memory." RAM would appear in Byte only in contrast with sequential access memory.

Shared memory mappings for devices

Posted May 11, 2018 16:44 UTC (Fri) by cladisch (✭ supporter ✭, #50193) [Link] (1 responses)

IDR is an ID allocator; the "R" stands for "radix tree", which is just an implementation detail.

IDA is an ID allocator that does not store a data poiner for each ID.

Shared memory mappings for devices

Posted May 14, 2018 13:16 UTC (Mon) by dezgeg (guest, #92243) [Link]

Maybe IDR could be made a backronym of say, "ID Registry" to hide the radix tree implementation detail.