On Sat 20-07-24 07:28:45, Qu Wenruo wrote: > > > 在 2024/7/19 20:43, Michal Hocko 写道: > > On Fri 19-07-24 19:58:39, Qu Wenruo wrote: > > > There is an incoming btrfs patchset, which will use @root_mem_cgroup as > > > the active cgroup to attach metadata folios to its internal btree > > > inode, so that btrfs can skip the possibly costly charge for the > > > internal inode which is only accessible by btrfs itself. > > > > > > However @root_mem_cgroup is not always defined (not defined for > > > CONFIG_MEMCG=n case), thus all such callers need to do the extra > > > handling for different CONFIG_MEMCG settings. > > > > > > So here we add a special macro definition of root_mem_cgroup, making it > > > to always be NULL. > > > > Isn't just a declaration sufficient? Nothing should really dereference > > the pointer anyway. > > > That can pass the compile, but waste the extra bytes for the pointer in > the data section, even if no one is utilizing that pointer. Are you sure that the mere declaration will be defined in the data section? -- Michal Hocko SUSE Labs
