Messages in this thread | | | Subject | Re: [PATCH] jffs2: safely remove obsolete dirent from the f->dents list | From | yuyufen <> | Date | Fri, 4 May 2018 17:27:22 +0800 |
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Hi, David. On 2018/5/4 16:18, David Woodhouse wrote: > > On Fri, 2018-05-04 at 16:06 +0800, yuyufen wrote: >>> You've made JFFS2_INVALID_LIMIT 64, which is reasonable enough >>> (although it's a bit of a weird name and possibly wants to be more >>> specific — invalid *what*?). >> Thansk a lot for your suggestions. >> >> Yes, it is really a bad name. How about JFFS2_OBS_DIRENT_LIMIT? I am >> not sure. > That'll do; at least it's a hint in the right direction :) > >>> So the maximum interesting value of ->obsolete_count is 64. Which means >>> it might as well be a uint8_t and sit in the padding after the >>> 'usercompr' field. >>> >>> It might be useful to look at putting the mutually exclusive fields in >>> struct jffs2_inode_info into a union, and then we don't need the >>> additional space of the atomic_t either; we'll never need that *and* >>> the fragtree at the same time... will we? >> You are right, thanks. But, obsolete_count may be large. So, I apply to >> use uint16_t and it also sits in the padding after the 'usercompr' >> field. > You can always just cap it. Once it reaches 64 it never changes again, > until you actually harvest them. Without that, a uint16_t could > overflow too.
I think 'JFFS2_OBS_DIRENT_LIMIT' may cause misunderstanding. Sorry for that. In my patch, it just means a threshold value. when ->nr_dir_opening is '0' and ->obsolete_count is bigger than the value, it can trigger removing operations.
If ->nr_dir_opening is not '0', obsolete_count may continuously increase and can exceed 64.
+static int jffs2_dir_release(struct inode *dir_i, struct file *filp) +{ +#ifndef CONFIG_JFFS2_SUMMARY + struct jffs2_inode_info *dir_f = JFFS2_INODE_INFO(dir_i); + + BUG_ON(atomic_read(&dir_f->nr_dir_opening) <= 0); + + mutex_lock(&dir_f->sem); + /* jffs2_dir_open may increase nr_dir_opening after + * atomic_dec_and_test() returning true. + * However, it cannot traverse the list until hold + * mutex dir_f->sem lock, so that we can go on +{ +#ifndef CONFIG_JFFS2_SUMMARY + struct jffs2_inode_info *dir_f = JFFS2_INODE_INFO(dir_i); + + BUG_ON(atomic_read(&dir_f->nr_dir_opening) <= 0); + + mutex_lock(&dir_f->sem); + /* jffs2_dir_open may increase nr_dir_opening after + * atomic_dec_and_test() returning true. + * However, it cannot traverse the list until hold + * mutex dir_f->sem lock, so that we can go on + * removing.*/ + if (atomic_dec_and_test(&dir_f->nr_dir_opening) && + dir_f->obsolete_count > JFFS2_OBS_DIRENT_LIMIT) { + struct jffs2_full_dirent **prev = &dir_f->dents; + + /* remove all obsolete dirent from the list, which + * can save memory space and reduce CPU time for + * traverse the list */ + while((*prev) && (dir_f->obsolete_count--)) { + if ((*prev)->raw == NULL && (*prev)->ino == 0) { + struct jffs2_full_dirent *this = *prev; + *prev = this->next; + jffs2_free_full_dirent(this); + } else + prev = &((*prev)->next); + } + } + mutex_unlock(&dir_f->sem); +#endif + + return 0; +}
Thanks, Yufen
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