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Date: Mon, 24 Feb 2014 12:28:07 +0900
From: Jaegeuk Kim <jaegeuk.kim@...sung.com>
To: Gu Zheng <guz.fnst@...fujitsu.com>
Cc: f2fs <linux-f2fs-devel@...ts.sourceforge.net>,
linux-kernel <linux-kernel@...r.kernel.org>,
fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] f2fs: simplify free nid management
Hi Gu,
The reason why I added the state of free nids was to avoid race
conditions.
[Without state transition]
Thread 1: Thread 2:
alloc_nid()
-> get a free nid : X alloc_nid()
-> remove X from the list
-> no free nids
build_free_nids()
-> add X into the list
--> X can be used by different two nodes, so I remained the allocated
nid, X, in the free nid list not to be added during build_free_nids().
Thanks,
2014-02-21 (금), 18:08 +0800, Gu Zheng:
> Previously, in the free nid management, we use two states to describe the state
> of a free nid entry:
> NID_NEW /* newly added to free nid list */
> NID_ALLOC /* it is allocated, but not really used*/
> When we alloc a new nid from free nid list,
> we just change the state from *NID_NEW* to *NID_ALLOC* and reduce the free nid
> count before complete success(nid_alloc).
> If we success finally, remove the nid entry from the free nid list(alloc_nid_done),
> else change the nid entry state to *NID_NEW* and increase the free nid count(alloc_nid_failed).
> As you know, the above three functions need to take free_nid_list_lock when search
> or remove the free nid entry.
> In the success path, we need to take free_nid_list_lock twice, one for finding
> and changing state, the other for removing the entry.
> And in the fail path, we need to take free_nid_list_lock twice too, one for finding
> and changing state, the other for finding and changing back the state.
> So you can see, the disign is not friendly to the success case, but to the fail
> case. And success case is more common than the fail case.
> So we simplify the free nid management to the following:
> Removed the nid entry state management.
> Removed the alloc nid done.
> alloc_nid will find a free nid and delete the entry from the free nid entry list.
> alloc_nid_faild will put back the free nid into the free nid entry list.
> With the above simplification, the success case will more neat, though the fail
> case will be a bit heavy.
> Besides, it also rename the function name for better descriptive.
> alloc_nid-->get_free_nid
> alloc_nid_failed-->put_back_free_nid
>
> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
> ---
> fs/f2fs/f2fs.h | 5 +--
> fs/f2fs/namei.c | 18 +++++----------
> fs/f2fs/node.c | 62 +++++++++++++++++++-----------------------------------
> fs/f2fs/node.h | 9 --------
> fs/f2fs/xattr.c | 11 ++++-----
> 5 files changed, 35 insertions(+), 70 deletions(-)
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 8cc7166..7fb6a83 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1129,9 +1129,8 @@ struct page *get_node_page(struct f2fs_sb_info *, pgoff_t);
> struct page *get_node_page_ra(struct page *, int);
> void sync_inode_page(struct dnode_of_data *);
> int sync_node_pages(struct f2fs_sb_info *, nid_t, struct writeback_control *);
> -bool alloc_nid(struct f2fs_sb_info *, nid_t *);
> -void alloc_nid_done(struct f2fs_sb_info *, nid_t);
> -void alloc_nid_failed(struct f2fs_sb_info *, nid_t);
> +bool get_free_nid(struct f2fs_sb_info *, nid_t *);
> +void put_back_free_nid(struct f2fs_sb_info *, nid_t);
> void recover_node_page(struct f2fs_sb_info *, struct page *,
> struct f2fs_summary *, struct node_info *, block_t);
> bool recover_xattr_data(struct inode *, struct page *, block_t);
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index 397d459..df956e9 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -34,7 +34,7 @@ static struct inode *f2fs_new_inode(struct inode *dir, umode_t mode)
> return ERR_PTR(-ENOMEM);
>
> f2fs_lock_op(sbi);
> - if (!alloc_nid(sbi, &ino)) {
> + if (!get_free_nid(sbi, &ino)) {
> f2fs_unlock_op(sbi);
> err = -ENOSPC;
> goto fail;
> @@ -75,7 +75,7 @@ fail:
> make_bad_inode(inode);
> iput(inode);
> if (nid_free)
> - alloc_nid_failed(sbi, ino);
> + put_back_free_nid(sbi, ino);
> return ERR_PTR(err);
> }
>
> @@ -137,8 +137,6 @@ static int f2fs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
> if (err)
> goto out;
>
> - alloc_nid_done(sbi, ino);
> -
> d_instantiate(dentry, inode);
> unlock_new_inode(inode);
> return 0;
> @@ -147,7 +145,7 @@ out:
> unlock_new_inode(inode);
> make_bad_inode(inode);
> iput(inode);
> - alloc_nid_failed(sbi, ino);
> + put_back_free_nid(sbi, ino);
> return err;
> }
>
> @@ -271,7 +269,6 @@ static int f2fs_symlink(struct inode *dir, struct dentry *dentry,
> goto out;
>
> err = page_symlink(inode, symname, symlen);
> - alloc_nid_done(sbi, inode->i_ino);
>
> d_instantiate(dentry, inode);
> unlock_new_inode(inode);
> @@ -281,7 +278,7 @@ out:
> unlock_new_inode(inode);
> make_bad_inode(inode);
> iput(inode);
> - alloc_nid_failed(sbi, inode->i_ino);
> + put_back_free_nid(sbi, inode->i_ino);
> return err;
> }
>
> @@ -309,8 +306,6 @@ static int f2fs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
> if (err)
> goto out_fail;
>
> - alloc_nid_done(sbi, inode->i_ino);
> -
> d_instantiate(dentry, inode);
> unlock_new_inode(inode);
>
> @@ -322,7 +317,7 @@ out_fail:
> unlock_new_inode(inode);
> make_bad_inode(inode);
> iput(inode);
> - alloc_nid_failed(sbi, inode->i_ino);
> + put_back_free_nid(sbi, inode->i_ino);
> return err;
> }
>
> @@ -360,7 +355,6 @@ static int f2fs_mknod(struct inode *dir, struct dentry *dentry,
> if (err)
> goto out;
>
> - alloc_nid_done(sbi, inode->i_ino);
> d_instantiate(dentry, inode);
> unlock_new_inode(inode);
> return 0;
> @@ -369,7 +363,7 @@ out:
> unlock_new_inode(inode);
> make_bad_inode(inode);
> iput(inode);
> - alloc_nid_failed(sbi, inode->i_ino);
> + put_back_free_nid(sbi, inode->i_ino);
> return err;
> }
>
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 8c5981e..7dc3246 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -396,7 +396,7 @@ int get_dnode_of_data(struct dnode_of_data *dn, pgoff_t index, int mode)
>
> if (!nids[i] && mode == ALLOC_NODE) {
> /* alloc new node */
> - if (!alloc_nid(sbi, &(nids[i]))) {
> + if (!get_free_nid(sbi, &(nids[i]))) {
> err = -ENOSPC;
> goto release_pages;
> }
> @@ -404,13 +404,12 @@ int get_dnode_of_data(struct dnode_of_data *dn, pgoff_t index, int mode)
> dn->nid = nids[i];
> npage[i] = new_node_page(dn, noffset[i], NULL);
> if (IS_ERR(npage[i])) {
> - alloc_nid_failed(sbi, nids[i]);
> + put_back_free_nid(sbi, nids[i]);
> err = PTR_ERR(npage[i]);
> goto release_pages;
> }
>
> set_nid(parent, offset[i - 1], nids[i], i == 1);
> - alloc_nid_done(sbi, nids[i]);
> done = true;
> } else if (mode == LOOKUP_NODE_RA && i == level && level > 1) {
> npage[i] = get_node_page_ra(parent, offset[i - 1]);
> @@ -1317,7 +1316,6 @@ static int add_free_nid(struct f2fs_nm_info *nm_i, nid_t nid, bool build)
>
> i = f2fs_kmem_cache_alloc(free_nid_slab, GFP_NOFS);
> i->nid = nid;
> - i->state = NID_NEW;
>
> spin_lock(&nm_i->free_nid_list_lock);
> if (__lookup_free_nid_list(nid, &nm_i->free_nid_list)) {
> @@ -1334,9 +1332,10 @@ static int add_free_nid(struct f2fs_nm_info *nm_i, nid_t nid, bool build)
> static void remove_free_nid(struct f2fs_nm_info *nm_i, nid_t nid)
> {
> struct free_nid *i;
> +
> spin_lock(&nm_i->free_nid_list_lock);
> i = __lookup_free_nid_list(nid, &nm_i->free_nid_list);
> - if (i && i->state == NID_NEW) {
> + if (i) {
> __del_from_free_nid_list(i);
> nm_i->fcnt--;
> }
> @@ -1416,11 +1415,10 @@ static void build_free_nids(struct f2fs_sb_info *sbi)
> * from second parameter of this function.
> * The returned nid could be used ino as well as nid when inode is created.
> */
> -bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
> +bool get_free_nid(struct f2fs_sb_info *sbi, nid_t *nid)
> {
> struct f2fs_nm_info *nm_i = NM_I(sbi);
> struct free_nid *i = NULL;
> - struct list_head *this;
> retry:
> if (unlikely(sbi->total_valid_node_count + 1 >= nm_i->max_nid))
> return false;
> @@ -1430,16 +1428,12 @@ retry:
> /* We should not use stale free nids created by build_free_nids */
> if (nm_i->fcnt && !on_build_free_nids(nm_i)) {
> f2fs_bug_on(list_empty(&nm_i->free_nid_list));
> - list_for_each(this, &nm_i->free_nid_list) {
> - i = list_entry(this, struct free_nid, list);
> - if (i->state == NID_NEW)
> - break;
> - }
>
> - f2fs_bug_on(i->state != NID_NEW);
> + i = list_first_entry(&nm_i->free_nid_list,
> + struct free_nid, list);
> *nid = i->nid;
> - i->state = NID_ALLOC;
> nm_i->fcnt--;
> + __del_from_free_nid_list(i);
> spin_unlock(&nm_i->free_nid_list_lock);
> return true;
> }
> @@ -1453,40 +1447,29 @@ retry:
> }
>
> /*
> - * alloc_nid() should be called prior to this function.
> + * get_free_nid() should be called prior to this function.
> */
> -void alloc_nid_done(struct f2fs_sb_info *sbi, nid_t nid)
> +void put_back_free_nid(struct f2fs_sb_info *sbi, nid_t nid)
> {
> struct f2fs_nm_info *nm_i = NM_I(sbi);
> - struct free_nid *i;
> -
> - spin_lock(&nm_i->free_nid_list_lock);
> - i = __lookup_free_nid_list(nid, &nm_i->free_nid_list);
> - f2fs_bug_on(!i || i->state != NID_ALLOC);
> - __del_from_free_nid_list(i);
> - spin_unlock(&nm_i->free_nid_list_lock);
> -}
> -
> -/*
> - * alloc_nid() should be called prior to this function.
> - */
> -void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
> -{
> - struct f2fs_nm_info *nm_i = NM_I(sbi);
> - struct free_nid *i;
> + struct free_nid *unused_nid;
>
> if (!nid)
> return;
>
> + unused_nid = f2fs_kmem_cache_alloc(free_nid_slab, GFP_NOFS);
> + unused_nid->nid = nid;
> +
> spin_lock(&nm_i->free_nid_list_lock);
> - i = __lookup_free_nid_list(nid, &nm_i->free_nid_list);
> - f2fs_bug_on(!i || i->state != NID_ALLOC);
> - if (nm_i->fcnt > 2 * MAX_FREE_NIDS) {
> - __del_from_free_nid_list(i);
> - } else {
> - i->state = NID_NEW;
> - nm_i->fcnt++;
> +
> + if (nm_i->fcnt > 2 * MAX_FREE_NIDS ||
> + __lookup_free_nid_list(nid, &nm_i->free_nid_list)) {
> + spin_unlock(&nm_i->free_nid_list_lock);
> + kmem_cache_free(free_nid_slab, unused_nid);
> + return;
> }
> + list_add_tail(&unused_nid->list, &nm_i->free_nid_list);
> + nm_i->fcnt++;
> spin_unlock(&nm_i->free_nid_list_lock);
> }
>
> @@ -1869,7 +1852,6 @@ void destroy_node_manager(struct f2fs_sb_info *sbi)
> /* destroy free nid list */
> spin_lock(&nm_i->free_nid_list_lock);
> list_for_each_entry_safe(i, next_i, &nm_i->free_nid_list, list) {
> - f2fs_bug_on(i->state == NID_ALLOC);
> __del_from_free_nid_list(i);
> nm_i->fcnt--;
> }
> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> index c4c7988..89221af 100644
> --- a/fs/f2fs/node.h
> +++ b/fs/f2fs/node.h
> @@ -71,18 +71,9 @@ static inline void node_info_from_raw_nat(struct node_info *ni,
> ni->version = raw_ne->version;
> }
>
> -/*
> - * For free nid mangement
> - */
> -enum nid_state {
> - NID_NEW, /* newly added to free nid list */
> - NID_ALLOC /* it is allocated */
> -};
> -
> struct free_nid {
> struct list_head list; /* for free node id list */
> nid_t nid; /* node id */
> - int state; /* in use or not: NID_NEW or NID_ALLOC */
> };
>
> static inline int next_free_nid(struct f2fs_sb_info *sbi, nid_t *nid)
> diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> index 89d0422..9f9741e 100644
> --- a/fs/f2fs/xattr.c
> +++ b/fs/f2fs/xattr.c
> @@ -337,7 +337,7 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
> inline_size = inline_xattr_size(inode);
>
> if (hsize > inline_size && !F2FS_I(inode)->i_xattr_nid)
> - if (!alloc_nid(sbi, &new_nid))
> + if (!get_free_nid(sbi, &new_nid))
> return -ENOSPC;
>
> /* write to inline xattr */
> @@ -350,7 +350,7 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
> } else {
> page = get_node_page(sbi, inode->i_ino);
> if (IS_ERR(page)) {
> - alloc_nid_failed(sbi, new_nid);
> + put_back_free_nid(sbi, new_nid);
> return PTR_ERR(page);
> }
> inline_addr = inline_xattr_addr(page);
> @@ -361,7 +361,7 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
> /* no need to use xattr node block */
> if (hsize <= inline_size) {
> err = truncate_xattr_node(inode, ipage);
> - alloc_nid_failed(sbi, new_nid);
> + put_back_free_nid(sbi, new_nid);
> return err;
> }
> }
> @@ -370,7 +370,7 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
> if (F2FS_I(inode)->i_xattr_nid) {
> xpage = get_node_page(sbi, F2FS_I(inode)->i_xattr_nid);
> if (IS_ERR(xpage)) {
> - alloc_nid_failed(sbi, new_nid);
> + put_back_free_nid(sbi, new_nid);
> return PTR_ERR(xpage);
> }
> f2fs_bug_on(new_nid);
> @@ -379,10 +379,9 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
> set_new_dnode(&dn, inode, NULL, NULL, new_nid);
> xpage = new_node_page(&dn, XATTR_NODE_OFFSET, ipage);
> if (IS_ERR(xpage)) {
> - alloc_nid_failed(sbi, new_nid);
> + put_back_free_nid(sbi, new_nid);
> return PTR_ERR(xpage);
> }
> - alloc_nid_done(sbi, new_nid);
> }
>
> xattr_addr = page_address(xpage);
--
Jaegeuk Kim
Samsung
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