Re: [PATCH 0/2] mm: skip memcg for certain address space

[Qu Wenruo <wqu@suse.com>]

Ping?

Any feedback?

I guess in this case btrfs is really the only one can benefit from this 
feature?

Thanks,
Qu

在 2024/7/10 10:37, Qu Wenruo 写道:
> Recently I'm hitting soft lockup if adding an order 2 folio to a
> filemap using GFP_NOFS | __GFP_NOFAIL. The softlockup happens at memcg
> charge code, and I guess that's exactly what __GFP_NOFAIL is expected to
> do, wait indefinitely until the request can be met.
> 
> On the other hand, if we do not use __GFP_NOFAIL, we can be limited by
> memcg at a lot of critical location, and lead to unnecessary transaction
> abort just due to memcg limit.
> 
> However for that specific btrfs call site, there is really no need charge
> the memcg, as that address space belongs to btree inode, which is not
> accessible to any end user, and that btree inode is a shared pool for
> all metadata of a btrfs.
> 
> So this patchset introduces a new address space flag, AS_NO_MEMCG, so
> that folios added to that address space will not trigger any memcg
> charge.
> 
> This would be the basis for future btrfs changes, like removing
> __GFP_NOFAIL completely and larger metadata folios.
> 
> Qu Wenruo (2):
>    mm: make lru_gen_eviction() to handle folios without memcg info
>    mm: allow certain address space to be not accounted by memcg
> 
>   fs/btrfs/disk-io.c      |  1 +
>   include/linux/pagemap.h |  1 +
>   mm/filemap.c            | 12 +++++++++---
>   mm/workingset.c         |  2 +-
>   4 files changed, 12 insertions(+), 4 deletions(-)
>