On 2019/11/20 23:45, Matthew Wilcox wrote: > On Wed, Nov 20, 2019 at 10:23:18PM +0800, zhengbin wrote: >> I have tried to change last_ino type to unsigned long, while this was >> rejected, see details on https://patchwork.kernel.org/patch/11023915. > Did you end up trying sbitmap? Maybe sbitmap is not a good solution, max_inodes of tmpfs are controlled by mount options--nrinodes, which can be modified by remountfs(bigger or smaller), as the comment of function sbitmap_resize says: * Doesn't reallocate anything. It's up to the caller to ensure that the new * depth doesn't exceed the depth that the sb was initialized with. We can modify this to meet the growing requirements, there will still be questions as follows: 1. tmpfs is a ram filesystem, we need to allocate sbitmap memory for sbinfo->max_inodes(while this maybe huge) 2.If remountfs changes max_inode, we have to deal with it, while this may take a long time (bigger: we need to free the old sbitmap memory, allocate new memory, copy the old sbitmap to new sbitmap smaller: How do we deal with it?ie: we use sb->map[inode number/8] to find the sbitmap, we need to change the exist inode numbers?while this maybe used by userspace application.) > > What I think is fundamentally wrong with this patch is that you've found a > problem in get_next_ino() and decided to use a different scheme for this > one filesystem, leaving every other filesystem which uses get_next_ino() > facing the same problem. > > That could be acceptable if you explained why tmpfs is fundamentally > different from all the other filesystems that use get_next_ino(), but > you haven't (and I don't think there is such a difference. eg pipes, > autofs and ipc mqueue could all have the same problem. tmpfs is same with all the other filesystems that use get_next_ino(), but we need to solve this problem one by one. If tmpfs is ok, we can modify the other filesystems too. Besides, I do not recommend all file systems share the same global variable, for performance impact consideration. > > There are some other problems I noticed, but they're not worth bringing > up until this fundamental design choice is justified. Agree, thanks. >
