On Sat, Feb 22, 2020 at 12:39:39PM -0800, Joe Perches wrote: > On Sat, 2020-02-22 at 23:15 +0300, Alexey Dobriyan wrote: > > Now that "struct proc_ops" exist we can start putting there stuff which > > could not fly with VFS "struct file_operations"... > > > > Most of fs/proc/inode.c file is dedicated to make open/read/.../close reliable > > in the event of disappearing /proc entries which usually happens if module is > > getting removed. Files like /proc/cpuinfo which never disappear simply do not > > need such protection. > > > > Save 2 atomic ops, 1 allocation, 1 free per open/read/close sequence for such > > "permanent" files. > > > > Enable "permanent" flag for > > > > /proc/cpuinfo > > /proc/kmsg > > /proc/modules > > /proc/slabinfo > > /proc/stat > > /proc/sysvipc/* > > /proc/swaps > > > > More will come once I figure out foolproof way to prevent out module > > authors from marking their stuff "permanent" for performance reasons > > when it is not. > > > > This should help with scalability: benchmark is "read /proc/cpuinfo R times > > by N threads scattered over the system". > > Is this an actual expected use-case? Yes. > Is there some additional unnecessary memory consumption > in the unscaled systems? No, it's the opposite. Less memory usage for everyone and noticeable performance improvement for contented case. > > static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) > > { > > struct proc_dir_entry *pde = PDE(file_inode(file)); > > ssize_t rv = -EIO; > > - if (use_pde(pde)) { > > - typeof_member(struct proc_ops, proc_read) read; > > > > - read = pde->proc_ops->proc_read; > > - if (read) > > - rv = read(file, buf, count, ppos); > > + if (pde_is_permanent(pde)) { > > + return pde_read(pde, file, buf, count, ppos); > > + } else if (use_pde(pde)) { > > + rv = pde_read(pde, file, buf, count, ppos); > > unuse_pde(pde); > > Perhaps all the function call duplication could be minimized > by using code without direct returns like: > > rv = pde_read(pde, file, buf, count, pos); > if (!pde_is_permanent(pde)) > unuse_pde(pde); > > return rv; Function call non-duplication is false goal. Surprisingly it makes code bigger: $ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux add/remove: 0/0 grow/shrink: 1/0 up/down: 10/0 (10) Function old new delta proc_reg_read 108 118 +10 and worse too: "rv" is carried on stack through "unuse_pde" call.