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Date: Wed, 21 Feb 2024 14:31:51 +0100
From: Jan Kara <jack@...e.cz>
To: Chuck Lever <cel@...nel.org>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
hughd@...gle.com, akpm@...ux-foundation.org,
Liam.Howlett@...cle.com, oliver.sang@...el.com, feng.tang@...el.com,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
maple-tree@...ts.infradead.org, linux-mm@...ck.org, lkp@...el.com
Subject: Re: [PATCH v2 6/6] libfs: Convert simple directory offsets to use a
Maple Tree
On Sat 17-02-24 15:24:16, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@...cle.com>
>
> Test robot reports:
> > kernel test robot noticed a -19.0% regression of aim9.disk_src.ops_per_sec on:
> >
> > commit: a2e459555c5f9da3e619b7e47a63f98574dc75f1 ("shmem: stable directory offsets")
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
> Feng Tang further clarifies that:
> > ... the new simple_offset_add()
> > called by shmem_mknod() brings extra cost related with slab,
> > specifically the 'radix_tree_node', which cause the regression.
>
> Willy's analysis is that, over time, the test workload causes
> xa_alloc_cyclic() to fragment the underlying SLAB cache.
>
> This patch replaces the offset_ctx's xarray with a Maple Tree in the
> hope that Maple Tree's dense node mode will handle this scenario
> more scalably.
>
> In addition, we can widen the simple directory offset maximum to
> signed long (as loff_t is also signed).
>
> Suggested-by: Matthew Wilcox <willy@...radead.org>
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202309081306.3ecb3734-oliver.sang@intel.com
> Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> fs/libfs.c | 47 +++++++++++++++++++++++------------------------
> include/linux/fs.h | 5 +++--
> 2 files changed, 26 insertions(+), 26 deletions(-)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index f7f92a49a418..d3d31197c8e4 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -245,17 +245,17 @@ enum {
> DIR_OFFSET_MIN = 2,
> };
>
> -static void offset_set(struct dentry *dentry, u32 offset)
> +static void offset_set(struct dentry *dentry, long offset)
> {
> - dentry->d_fsdata = (void *)((uintptr_t)(offset));
> + dentry->d_fsdata = (void *)offset;
> }
>
> -static u32 dentry2offset(struct dentry *dentry)
> +static long dentry2offset(struct dentry *dentry)
> {
> - return (u32)((uintptr_t)(dentry->d_fsdata));
> + return (long)dentry->d_fsdata;
> }
>
> -static struct lock_class_key simple_offset_xa_lock;
> +static struct lock_class_key simple_offset_lock_class;
>
> /**
> * simple_offset_init - initialize an offset_ctx
> @@ -264,8 +264,8 @@ static struct lock_class_key simple_offset_xa_lock;
> */
> void simple_offset_init(struct offset_ctx *octx)
> {
> - xa_init_flags(&octx->xa, XA_FLAGS_ALLOC1);
> - lockdep_set_class(&octx->xa.xa_lock, &simple_offset_xa_lock);
> + mt_init_flags(&octx->mt, MT_FLAGS_ALLOC_RANGE);
> + lockdep_set_class(&octx->mt.ma_lock, &simple_offset_lock_class);
> octx->next_offset = DIR_OFFSET_MIN;
> }
>
> @@ -274,20 +274,19 @@ void simple_offset_init(struct offset_ctx *octx)
> * @octx: directory offset ctx to be updated
> * @dentry: new dentry being added
> *
> - * Returns zero on success. @so_ctx and the dentry offset are updated.
> + * Returns zero on success. @octx and the dentry's offset are updated.
> * Otherwise, a negative errno value is returned.
> */
> int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
> {
> - static const struct xa_limit limit = XA_LIMIT(DIR_OFFSET_MIN, U32_MAX);
> - u32 offset;
> + unsigned long offset;
> int ret;
>
> if (dentry2offset(dentry) != 0)
> return -EBUSY;
>
> - ret = xa_alloc_cyclic(&octx->xa, &offset, dentry, limit,
> - &octx->next_offset, GFP_KERNEL);
> + ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN,
> + LONG_MAX, &octx->next_offset, GFP_KERNEL);
> if (ret < 0)
> return ret;
>
> @@ -303,13 +302,13 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
> */
> void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
> {
> - u32 offset;
> + long offset;
>
> offset = dentry2offset(dentry);
> if (offset == 0)
> return;
>
> - xa_erase(&octx->xa, offset);
> + mtree_erase(&octx->mt, offset);
> offset_set(dentry, 0);
> }
>
> @@ -332,7 +331,7 @@ int simple_offset_empty(struct dentry *dentry)
>
> index = DIR_OFFSET_MIN;
> octx = inode->i_op->get_offset_ctx(inode);
> - xa_for_each(&octx->xa, index, child) {
> + mt_for_each(&octx->mt, child, index, LONG_MAX) {
> spin_lock(&child->d_lock);
> if (simple_positive(child)) {
> spin_unlock(&child->d_lock);
> @@ -362,8 +361,8 @@ int simple_offset_rename_exchange(struct inode *old_dir,
> {
> struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir);
> struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir);
> - u32 old_index = dentry2offset(old_dentry);
> - u32 new_index = dentry2offset(new_dentry);
> + long old_index = dentry2offset(old_dentry);
> + long new_index = dentry2offset(new_dentry);
> int ret;
>
> simple_offset_remove(old_ctx, old_dentry);
> @@ -389,9 +388,9 @@ int simple_offset_rename_exchange(struct inode *old_dir,
>
> out_restore:
> offset_set(old_dentry, old_index);
> - xa_store(&old_ctx->xa, old_index, old_dentry, GFP_KERNEL);
> + mtree_store(&old_ctx->mt, old_index, old_dentry, GFP_KERNEL);
> offset_set(new_dentry, new_index);
> - xa_store(&new_ctx->xa, new_index, new_dentry, GFP_KERNEL);
> + mtree_store(&new_ctx->mt, new_index, new_dentry, GFP_KERNEL);
> return ret;
> }
>
> @@ -404,7 +403,7 @@ int simple_offset_rename_exchange(struct inode *old_dir,
> */
> void simple_offset_destroy(struct offset_ctx *octx)
> {
> - xa_destroy(&octx->xa);
> + mtree_destroy(&octx->mt);
> }
>
> /**
> @@ -434,16 +433,16 @@ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence)
>
> /* In this case, ->private_data is protected by f_pos_lock */
> file->private_data = NULL;
> - return vfs_setpos(file, offset, U32_MAX);
> + return vfs_setpos(file, offset, LONG_MAX);
> }
>
> static struct dentry *offset_find_next(struct offset_ctx *octx, loff_t offset)
> {
> + MA_STATE(mas, &octx->mt, offset, offset);
> struct dentry *child, *found = NULL;
> - XA_STATE(xas, &octx->xa, offset);
>
> rcu_read_lock();
> - child = xas_next_entry(&xas, U32_MAX);
> + child = mas_find(&mas, LONG_MAX);
> if (!child)
> goto out;
> spin_lock(&child->d_lock);
> @@ -457,8 +456,8 @@ static struct dentry *offset_find_next(struct offset_ctx *octx, loff_t offset)
>
> static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry)
> {
> - u32 offset = dentry2offset(dentry);
> struct inode *inode = d_inode(dentry);
> + long offset = dentry2offset(dentry);
>
> return ctx->actor(ctx, dentry->d_name.name, dentry->d_name.len, offset,
> inode->i_ino, fs_umode_to_dtype(inode->i_mode));
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 03d141809a2c..55144c12ee0f 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -43,6 +43,7 @@
> #include <linux/cred.h>
> #include <linux/mnt_idmapping.h>
> #include <linux/slab.h>
> +#include <linux/maple_tree.h>
>
> #include <asm/byteorder.h>
> #include <uapi/linux/fs.h>
> @@ -3260,8 +3261,8 @@ extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
> const void __user *from, size_t count);
>
> struct offset_ctx {
> - struct xarray xa;
> - u32 next_offset;
> + struct maple_tree mt;
> + unsigned long next_offset;
> };
>
> void simple_offset_init(struct offset_ctx *octx);
>
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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