Messages in this thread | | | Subject | Re: [PATCH v3] proc: faster open/read/close with "permanent" files | From | Joe Perches <> | Date | Sat, 22 Feb 2020 12:39:39 -0800 |
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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? Is there some additional unnecessary memory consumption in the unscaled systems?
And trivia:
> static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence) > { [] > + if (pde_is_permanent(pde)) { > + return pde_lseek(pde, file, offset, whence); > + } else if (use_pde(pde)) { > + rv = pde_lseek(pde, file, offset, whence); > unuse_pde(pde); > } > return rv; > } [] > 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;
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