On 11/12/22 05:46, Conor Dooley wrote: > On Fri, Nov 11, 2022 at 11:33:30AM +0100, Vlastimil Babka wrote: >> On 11/8/22 22:44, Pasha Tatashin wrote: >>> On Tue, Nov 8, 2022 at 10:55 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: >>>> >>>> Hi, >>>> >>>> as we all know, we currently have three slab allocators. As we discussed >>>> at LPC [1], it is my hope that one of these allocators has a future, and >>>> two of them do not. >>>> >>>> The unsurprising reasons include code maintenance burden, other features >>>> compatible with only a subset of allocators (or more effort spent on the >>>> features), blocking API improvements (more on that below), and my >>>> inability to pronounce SLAB and SLUB in a properly distinguishable way, >>>> without resorting to spelling out the letters. >>>> >>>> I think (but may be proven wrong) that SLOB is the easier target of the >>>> two to be removed, so I'd like to focus on it first. >>>> >>>> I believe SLOB can be removed because: >>>> >>>> - AFAIK nobody really uses it? It strives for minimal memory footprint >>>> by putting all objects together, which has its CPU performance costs >>>> (locking, lack of percpu caching, searching for free space...). I'm not >>>> aware of any "tiny linux" deployment that opts for this. For example, >>>> OpenWRT seems to use SLUB and the devices these days have e.g. 128MB >>>> RAM, not up to 16 MB anymore. I've heard anecdotes that the performance >>>> SLOB impact is too much for those who tried. Googling for >>>> "CONFIG_SLOB=y" yielded nothing useful. >>> >>> I am all for removing SLOB. >>> >>> There are some devices with configs where SLOB is enabled by default. >>> Perhaps, the owners/maintainers of those devices/configs should be >>> included into this thread: >>> >>> tatashin@soleen:~/x/linux$ git grep SLOB=y > >>> arch/riscv/configs/nommu_k210_defconfig:CONFIG_SLOB=y >>> arch/riscv/configs/nommu_k210_sdcard_defconfig:CONFIG_SLOB=y >>> arch/riscv/configs/nommu_virt_defconfig:CONFIG_SLOB=y > >> >> Turns out that since SLOB depends on EXPERT, many of those lack it so >> running make defconfig ends up with SLUB anyway, unless I miss something. >> Only a subset has both SLOB and EXPERT: >> >>> git grep CONFIG_EXPERT `git grep -l "CONFIG_SLOB=y"` > >> arch/riscv/configs/nommu_virt_defconfig:CONFIG_EXPERT=y > > I suppose there's not really a concern with the virt defconfig, but I > did check the output of `make nommu_k210_defconfig" and despite not > having expert it seems to end up CONFIG_SLOB=y in the generated .config. > > I do have a board with a k210 so I checked with s/SLOB/SLUB and it still > boots etc, but I have no workloads or w/e to run on it. I will try with SLUB over the weekend. -- Damien Le Moal Western Digital Research
