Messages in this thread Patch in this message |  | | Subject | Re: [PATCH v5 1/2] tmpfs: Add per-superblock i_ino support | From | "zhengbin (A)" <> | Date | Mon, 6 Jan 2020 10:03:57 +0800 |
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On 2020/1/5 20:06, Chris Down wrote: > get_next_ino has a number of problems: > > - It uses and returns a uint, which is susceptible to become overflowed > if a lot of volatile inodes that use get_next_ino are created. > - It's global, with no specificity per-sb or even per-filesystem. This > means it's not that difficult to cause inode number wraparounds on a > single device, which can result in having multiple distinct inodes > with the same inode number. > > This patch adds a per-superblock counter that mitigates the second case. > This design also allows us to later have a specific i_ino size > per-device, for example, allowing users to choose whether to use 32- or > 64-bit inodes for each tmpfs mount. This is implemented in the next > commit. > > Signed-off-by: Chris Down <chris@chrisdown.name> > Reviewed-by: Amir Goldstein <amir73il@gmail.com> > Cc: Hugh Dickins <hughd@google.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Al Viro <viro@zeniv.linux.org.uk> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Jeff Layton <jlayton@kernel.org> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Tejun Heo <tj@kernel.org> > Cc: linux-mm@kvack.org > Cc: linux-fsdevel@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: kernel-team@fb.com > --- > include/linux/shmem_fs.h | 1 + > mm/shmem.c | 30 +++++++++++++++++++++++++++++- > 2 files changed, 30 insertions(+), 1 deletion(-) > > v5: Nothing in code, just resending with correct linux-mm domain. > > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > index de8e4b71e3ba..7fac91f490dc 100644 > --- a/include/linux/shmem_fs.h > +++ b/include/linux/shmem_fs.h > @@ -35,6 +35,7 @@ struct shmem_sb_info { > unsigned char huge; /* Whether to try for hugepages */ > kuid_t uid; /* Mount uid for root directory */ > kgid_t gid; /* Mount gid for root directory */ > + ino_t next_ino; /* The next per-sb inode number to use */ > struct mempolicy *mpol; /* default memory policy for mappings */ > spinlock_t shrinklist_lock; /* Protects shrinklist */ > struct list_head shrinklist; /* List of shinkable inodes */ > diff --git a/mm/shmem.c b/mm/shmem.c > index 8793e8cc1a48..9e97ba972225 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2236,6 +2236,12 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma) > return 0; > } > > +/* > + * shmem_get_inode - reserve, allocate, and initialise a new inode > + * > + * If this tmpfs is from kern_mount we use get_next_ino, which is global, since > + * inum churn there is low and this avoids taking locks. > + */ > static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir, > umode_t mode, dev_t dev, unsigned long flags) > { > @@ -2248,7 +2254,28 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode > > inode = new_inode(sb); > if (inode) { > - inode->i_ino = get_next_ino(); > + if (sb->s_flags & SB_KERNMOUNT) { > + /* > + * __shmem_file_setup, one of our callers, is lock-free: > + * it doesn't hold stat_lock in shmem_reserve_inode > + * since max_inodes is always 0, and is called from > + * potentially unknown contexts. As such, use the global > + * allocator which doesn't require the per-sb stat_lock. > + */ > + inode->i_ino = get_next_ino(); > + } else { > + spin_lock(&sbinfo->stat_lock);
Use spin_lock will affect performance, how about define
unsigned long __percpu *last_ino_number; /* Last inode number */ atomic64_t shared_last_ino_number; /* Shared last inode number */ in shmem_sb_info, whose performance will be better?
> + if (unlikely(sbinfo->next_ino > UINT_MAX)) { > + /* > + * Emulate get_next_ino uint wraparound for > + * compatibility > + */ > + sbinfo->next_ino = 1; > + } > + inode->i_ino = sbinfo->next_ino++; > + spin_unlock(&sbinfo->stat_lock); > + } > + > inode_init_owner(inode, dir, mode); > inode->i_blocks = 0; > inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); > @@ -3662,6 +3689,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc) > #else > sb->s_flags |= SB_NOUSER; > #endif > + sbinfo->next_ino = 1; > sbinfo->max_blocks = ctx->blocks; > sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes; > sbinfo->uid = ctx->uid;
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