Re: [RFC PATCH v1 15/17] blk-cgroup: remove blkg radix tree preloading

Hi,

=E5=9C=A8 2026/7/9 14:18, Christoph Hellwig =E5=86=99=E9=81=93:
> On Sun, Jul 05, 2026 at 03:51:22AM +0800, Yu Kuai wrote:
>> From: Yu Kuai <[email protected]>
>>
>> blkg creation is now serialized by q->blkcg_mutex and no longer runs
>> under q->queue_lock.  The radix tree is initialized with GFP_NOWAIT, so
>> radix_tree_insert() cannot sleep while blkcg->lock is held and the old
>> preload dance is no longer needed.
>>
>> Remove the preload calls and the associated unwind path.
> Isn't the GFP_NOWAIT a bit of a problem because it can fail way too
> easy?

I think GFP_NOWAIT should not be a problem because it's only possible to
allocate blkg when the thread is issuing the first IO. And it's not a big
deal to fail nowait in this case because the caller should fall back to
sleepable context to issue this IO, and then blkg will be created. The foll=
owing
nowait IO issued by this thread should no longer hit blkg allocation path
anymore.

>
> What about converting both the radix tree and list to an xarray
> using the internal xarray to deal with sleeping allocations?
>
--=20
Thanks,
Kuai