Re: [PATCH v2 0/5] Move kvfree_rcu() into SLAB (v2)

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Dec 16, 2024 at 03:20:44PM +0100, Vlastimil Babka wrote:
> On 12/16/24 12:03, Uladzislau Rezki wrote:
> > On Sun, Dec 15, 2024 at 06:30:02PM +0100, Vlastimil Babka wrote:
> >> On 12/12/24 19:02, Uladzislau Rezki (Sony) wrote:
> >> > Hello!
> >> > 
> >> > This is v2. It is based on the Linux 6.13-rc2. The first version is
> >> > here:
> >> > 
> >> > https://lore.kernel.org/linux-mm/20241210164035.3391747-4-urezki@gmail.com/T/
> >> > 
> >> > The difference between v1 and v2 is that, the preparation process is
> >> > done in original place instead and after that there is one final move.
> >> 
> >> Looks good, will include in slab/for-next
> >> 
> >> I think patch 5 should add more explanation to the commit message - the
> >> subthread started by Christoph could provide content :) Can you summarize so
> >> I can amend the commit log?
> >> 
> > I will :)
> > 
> >> Also how about a followup patch moving the rcu-tiny implementation of
> >> kvfree_call_rcu()?
> >> 
> > As, Paul already noted, it would make sense. Or just remove a tiny
> > implementation.
> 
> AFAICS tiny rcu is for !SMP systems. Do they benefit from the "full"
> implementation with all the batching etc or would that be unnecessary overhead?
> 
Yes, it is for a really small systems with low amount of memory. I see
only one overhead it is about driving objects in pages. For a small
system it can be critical because we allocate.

From the other hand, for a tiny variant we can modify the normal variant
by bypassing batching logic, thus do not consume memory(for Tiny case)
i.e. merge it to a normal kvfree_rcu() path.

After that we do not depend on CONFIG_RCU_TINY option. Probably we need
also to perform some adaptation of regular kvfree_rcu() for a single CPU
system.

--
Uladzislau Rezki