Hi, you should have Ccd people according to get_maintainers script to get a reply faster. Let me Cc the MEMCG section. On 7/10/24 3:07 AM, Qu Wenruo wrote: > 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. Seems like a bug to me, as the charging of __GFP_NOFAIL in try_charge_memcg() should proceed to the force: part AFAICS and just go over the limit. I was suspecting mem_cgroup_oom() a bit earlier return true, causing the retry loop, due to GFP_NOFS. But it seems out_of_memory() should be specifically proceeding for GFP_NOFS if it's memcg oom. But I might be missing something else. Anyway we should know what exactly is going first. > 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(-) >
