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Date: Fri, 23 Jan 2015 14:15:56 +0800
From: Chao Yu <chao2.yu@...sung.com>
To: 'Jaegeuk Kim' <jaegeuk@...nel.org>
Cc: 'Changman Lee' <cm224.lee@...sung.com>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: RE: [f2fs-dev][RFC PATCH 06/10] f2fs: add core functions for rb-tree
extent cache
Hi Jaegeuk,
> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Friday, January 23, 2015 9:48 AM
> To: Chao Yu
> Cc: Changman Lee; linux-f2fs-devel@...ts.sourceforge.net; linux-kernel@...r.kernel.org
> Subject: Re: [f2fs-dev][RFC PATCH 06/10] f2fs: add core functions for rb-tree extent cache
>
> On Mon, Jan 12, 2015 at 03:14:48PM +0800, Chao Yu wrote:
> > This patch adds core functions including slab cache init function and
> > init/lookup/update/shrink/destroy function for rb-tree based extent cache.
> >
> > Thank Jaegeuk Kim and Changman Lee as they gave much suggestion about detail
> > design and implementation of extent cache.
> >
> > Todo:
> > * add a cached_ei into struct extent_tree for a quick recent cache.
> > * register rb-based extent cache shrink with mm shrink interface.
> > * disable dir inode's extent cache.
> >
> > Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > Signed-off-by: Changman Lee <cm224.lee@...sung.com>
> > ---
> > fs/f2fs/data.c | 458 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > fs/f2fs/node.c | 9 +-
> > 2 files changed, 466 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 4f5b871e..bf8c5eb 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -25,6 +25,9 @@
> > #include "trace.h"
> > #include <trace/events/f2fs.h>
> >
> > +struct kmem_cache *extent_tree_slab;
> > +struct kmem_cache *extent_node_slab;
> > +
> > static void f2fs_read_end_io(struct bio *bio, int err)
> > {
> > struct bio_vec *bvec;
> > @@ -373,6 +376,430 @@ end_update:
> > return need_update;
> > }
> >
> > +static struct extent_node *__lookup_extent_tree(struct extent_tree *et,
> > + unsigned int fofs)
> > +{
> > + struct rb_node *node = et->root.rb_node;
> > + struct extent_node *en;
> > +
> > + while (node) {
> > + en = rb_entry(node, struct extent_node, rb_node);
> > + if (fofs < en->ei.fofs)
> > + node = node->rb_left;
> > + else if (fofs >= en->ei.fofs + en->ei.len)
> > + node = node->rb_right;
> > + else
> > + return en;
> > + }
> > + return NULL;
> > +}
> > +
> > +static inline void set_extent_info(struct extent_info *ei, unsigned int fofs,
> > + u32 blk, unsigned int len)
> > +{
> > + ei->fofs = fofs;
> > + ei->blk = blk;
> > + ei->len = len;
> > +}
> > +
> > +static inline bool __is_extent_mergeable(struct extent_info *back,
> > + struct extent_info *front)
> > +{
> > + return (back->fofs + back->len == front->fofs &&
> > + back->blk + back->len == front->blk);
> > +}
> > +
> > +static bool __is_back_mergeable(struct extent_info *cur,
> > + struct extent_info *back)
> > +{
> > + return __is_extent_mergeable(back, cur);
> > +}
> > +
> > +static bool __is_front_mergeable(struct extent_info *cur,
> > + struct extent_info *front)
> > +{
> > + return __is_extent_mergeable(cur, front);
> > +}
>
>
> How about declaring these four functions as inline ones and locating them
> inside f2fs.h?
Good idea! Will do.
>
> > +
> > +static struct extent_node *__try_back_merge(struct extent_tree *et,
> > + struct extent_node *en)
> > +{
> > + struct extent_node *prev;
> > + struct rb_node *node;
> > +
> > + node = rb_prev(&en->rb_node);
> > + if (!node)
> > + return NULL;
> > +
> > + prev = rb_entry(node, struct extent_node, rb_node);
> > + if (__is_back_mergeable(&en->ei, &prev->ei)) {
> > + en->ei.fofs = prev->ei.fofs;
> > + en->ei.blk = prev->ei.blk;
> > + en->ei.len += prev->ei.len;
> > + rb_erase(&prev->rb_node, &et->root);
> > + et->count--;
> > + return prev;
> > + }
> > + return NULL;
> > +}
> > +
> > +static struct extent_node *__try_front_merge(struct extent_tree *et,
> > + struct extent_node *en)
> > +{
> > + struct extent_node *next;
> > + struct rb_node *node;
> > +
> > + node = rb_next(&en->rb_node);
> > + if (!node)
> > + return NULL;
> > +
> > + next = rb_entry(node, struct extent_node, rb_node);
> > + if (__is_front_mergeable(&en->ei, &next->ei)) {
> > + en->ei.len += next->ei.len;
> > + rb_erase(&next->rb_node, &et->root);
> > + et->count--;
> > + return next;
> > + }
> > + return NULL;
> > +}
> > +
> > +static struct extent_node *__insert_extent_tree(struct f2fs_sb_info *sbi,
> > + struct extent_tree *et, struct extent_info *ei,
> > + struct extent_node **den)
> > +{
> > + struct rb_node **p = &et->root.rb_node;
> > + struct rb_node *parent = NULL;
> > + struct extent_node *en;
> > +
> > + while (*p) {
> > + parent = *p;
> > + en = rb_entry(parent, struct extent_node, rb_node);
> > +
> > + if (ei->fofs < en->ei.fofs) {
> > + if (__is_front_mergeable(ei, &en->ei)) {
> > + f2fs_bug_on(sbi, !den);
> > + en->ei.fofs = ei->fofs;
> > + en->ei.blk = ei->blk;
> > + en->ei.len += ei->len;
> > + *den = __try_back_merge(et, en);
> > + return en;
> > + }
> > + p = &(*p)->rb_left;
> > + } else if (ei->fofs >= en->ei.fofs + en->ei.len) {
> > + if (__is_back_mergeable(ei, &en->ei)) {
> > + f2fs_bug_on(sbi, !den);
> > + en->ei.len += ei->len;
> > + *den = __try_front_merge(et, en);
> > + return en;
> > + }
> > + p = &(*p)->rb_right;
> > + } else
> > + f2fs_bug_on(F2FS_I_SB(inode), 1);
>
> Coding style.
>
> } else {
> ...
> }
will fix.
>
> > + }
>
> How about adding __attach_extent_node()?
That's more readable.
How do you think of the following functions:
struct extent_node *__attach_extent_node(struct f2fs_sb_info *sbi,
struct extent_tree *et, struct extent_info *ei,
struct rb_node *parent, struct rb_node **p)
{
struct extent_node *en;
en = kmem_cache_alloc(extent_node_slab, GFP_ATOMIC);
if (!en)
return NULL;
en->ei = *ei;
INIT_LIST_HEAD(&en->list);
rb_link_node(&en->rb_node, parent, p);
rb_insert_color(&en->rb_node, &et->root);
et->count++;
atomic_inc(&sbi->total_ext_node);
return en;
}
static void __detach_extent_node(struct f2fs_sb_info *sbi,
struct extent_tree *et, struct extent_node *en)
{
rb_erase(&en->rb_node, &et->root);
et->count--;
atomic_dec(&sbi->total_ext_node);
}
> {
> > +
> > + en = kmem_cache_alloc(extent_node_slab, GFP_ATOMIC);
>
> en = f2fs_kmem_cache_alloc(.., GFP_ATOMIC);
We should avoid cond_resched() in f2fs_kmem_cache_alloc when we are holding write_lock.
IMO, it's better to return NULL if we fail to alloc extent_node here.
Otherwise we'd better alloc extent_node before write_lock.
>
> > + en->ei = *ei;
> > + INIT_LIST_HEAD(&en->list);
> > +
> > + rb_link_node(&en->rb_node, parent, p);
> > + rb_insert_color(&en->rb_node, &et->root);
> > + atomic_inc(&sbi->total_ext_node);
> > + et->count++;
>
> }
>
> > +
> > + return en;
> > +}
> > +
> > +static struct extent_node *__remove_extent_tree(struct extent_tree *et,
> > + unsigned int fofs)
>
> This is __detach_extent_node()?
>
> > +{
> > + struct rb_node *p = et->root.rb_node;
> > + struct extent_node *en;
> > +
> > + while (p) {
> > + en = rb_entry(p, struct extent_node, rb_node);
> > +
> > + if (fofs < en->ei.fofs)
> > + p = p->rb_left;
>
> Coding style.
>
> if () {
> } else {
> }
will fix.
>
> > + else if (fofs >= en->ei.fofs + en->ei.len)
> > + p = p->rb_right;
> > + else {
> > + rb_erase(&en->rb_node, &et->root);
> > + et->count--;
>
> Add here?
> atomic_dec(&sbi->total_ext_node);
Agree, see __detach_extent_node() implementation above.
>
> > + return en;
> > + }
> > + }
> > + return NULL;
> > +}
> > +
> > +static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
> > + struct extent_tree *et, bool free_all)
> > +{
> > + struct rb_node *node, *next;
> > + struct extent_node *en;
> > + unsigned int count = et->count;
> > +
> > + node = rb_first(&et->root);
> > + while (node) {
> > + next = rb_next(node);
> > + en = rb_entry(node, struct extent_node, rb_node);
> > +
> > + if (free_all) {
> > + spin_lock(&sbi->extent_lock);
> > + if (!list_empty(&en->list))
> > + list_del_init(&en->list);
> > + spin_unlock(&sbi->extent_lock);
> > + }
> > +
> > + if (free_all || list_empty(&en->list)) {
> > + rb_erase(node, &et->root);
> > + kmem_cache_free(extent_node_slab, en);
> > + atomic_dec(&sbi->total_ext_node);
> > + et->count--;
> > + }
> > + node = next;
> > + }
> > +
> > + return count - et->count;
> > +}
> > +
> > +static bool f2fs_lookup_extent_tree(struct inode *inode, pgoff_t pgofs,
> > + struct extent_info *ei)
> > +{
> > + struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> > + struct extent_tree *et;
> > + struct extent_node *en;
> > +
> > + if (is_inode_flag_set(F2FS_I(inode), FI_NO_EXTENT))
> > + return false;
> > +
> > + down_read(&sbi->extent_tree_lock);
> > + et = radix_tree_lookup(&sbi->extent_tree_root, inode->i_ino);
> > + if (!et) {
> > + up_read(&sbi->extent_tree_lock);
> > + return false;
> > + }
> > + atomic_inc(&et->refcount);
> > + up_read(&sbi->extent_tree_lock);
> > +
> > + read_lock(&et->lock);
> > + en = __lookup_extent_tree(et, pgofs);
> > + if (en) {
> > + *ei = en->ei;
> > + spin_lock(&sbi->extent_lock);
> > + if (!list_empty(&en->list))
> > + list_move_tail(&en->list, &sbi->extent_list);
> > + spin_unlock(&sbi->extent_lock);
> > + stat_inc_read_hit(sbi->sb);
> > + }
> > + stat_inc_total_hit(sbi->sb);
> > + read_unlock(&et->lock);
> > +
> > + atomic_dec(&et->refcount);
> > + return en ? true : false;
> > +}
> > +
> > +static void f2fs_update_extent_tree(struct inode *inode, pgoff_t fofs,
> > + block_t blkaddr)
> > +{
> > + struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> > + nid_t ino = inode->i_ino;
> > + struct extent_tree *et;
> > + struct extent_node *en = NULL, *en1 = NULL, *en2 = NULL, *en3 = NULL;
> > + struct extent_node *den = NULL;
> > + struct extent_info *pei;
> > + struct extent_info ei;
> > + unsigned int endofs;
> > +
> > + if (is_inode_flag_set(F2FS_I(inode), FI_NO_EXTENT))
> > + return;
> > +
> > +retry:
> > + down_write(&sbi->extent_tree_lock);
> > + et = radix_tree_lookup(&sbi->extent_tree_root, ino);
> > + if (!et) {
> > + et = kmem_cache_alloc(extent_tree_slab, GFP_ATOMIC);
>
> et = f2fs_kmem_cache_alloc(.., GFP_ATOMIC);
How about modifying as below to avoid holding extent_tree_lock for long time?
et = kmem_cache_alloc(extent_tree_slab, GFP_ATOMIC);
if (!et) {
up_write(&sbi->extent_tree_lock);
cond_resched();
goto retry;
}
>
> > + if (!et) {
> > + up_write(&sbi->extent_tree_lock);
> > + goto retry;
> > + }
> > + if (radix_tree_insert(&sbi->extent_tree_root, ino, et)) {
> > + up_write(&sbi->extent_tree_lock);
> > + kmem_cache_free(extent_tree_slab, et);
cond_resched()?
> > + goto retry;
> > + }
> > + memset(et, 0, sizeof(struct extent_tree));
> > + et->ino = ino;
> > + et->root = RB_ROOT;
> > + rwlock_init(&et->lock);
> > + atomic_set(&et->refcount, 0);
> > + et->count = 0;
> > + sbi->total_ext_tree++;
> > + }
> > + atomic_inc(&et->refcount);
> > + up_write(&sbi->extent_tree_lock);
> > +
> > + write_lock(&et->lock);
> > +
> > + /* 1. lookup and remove exist extent info in cache */
>
> existing
got it.
>
> > + en = __remove_extent_tree(et, fofs);
>
> en = __detach_extent_node();?
OK, it seems that most codes of __remove_extent_tree and __lookup_extent_tree
are the same, so here I want to remove extent node like this:
en = __lookup_extent_tree(et, fofs);
if (!en)
goto update_extent;
dei = en->ei;
__detach_extent_node(sbi, et, en);
How do you think?
>
> > + if (!en)
> > + goto update_extent;
> > +
> > + pei = &en->ei;
> > + /* 2. if extent can be split more, split and insert the left part */
> > + if (pei->len > 1) {
> > + /* insert left part of split extent into cache */
> > + if (pei->fofs < fofs) {
> > + set_extent_info(&ei, pei->fofs, pei->blk,
> > + fofs - pei->fofs);
> > + en1 = __insert_extent_tree(sbi, et, &ei, NULL);
> > + }
> > +
> > + /* insert right part of split extent into cache */
> > + endofs = pei->fofs + pei->len - 1;
> > + if (endofs > fofs) {
> > + set_extent_info(&ei, fofs + 1,
> > + fofs - pei->fofs + pei->blk, endofs - fofs);
> > + en2 = __insert_extent_tree(sbi, et, &ei, NULL);
> > + }
> > + }
> > +
> > +update_extent:
> > + /* 3. update extent in extent cache */
> > + if (blkaddr) {
> > + set_extent_info(&ei, fofs, blkaddr, 1);
> > + en3 = __insert_extent_tree(sbi, et, &ei, &den);
> > + }
> > +
> > + /* 4. update in global extent list */
> > + spin_lock(&sbi->extent_lock);
> > + if (en && !list_empty(&en->list))
> > + list_del_init(&en->list);
> > + /*
> > + * en1 and en2 split from en, they will become more and more smaller
> > + * fragments after splitting several times. So if the length is smaller
> > + * than F2FS_MIN_EXTENT_LEN, we will not add them into extent_list,
> > + * but just waiting shrinker to free them for reclaiming when OOM.
> > + */
>
> Can we just remove en1 and en2 in __insert_extent_tree?
en1 and en2 is newly added, in __attach_extent_node we do not add en1 and en2 into
lru list, so if you do not want to keep split part in lru list, let's just remove
the below codes.
>
> > + if (en1 && en1->ei.len >= F2FS_MIN_EXTENT_LEN)
> > + list_add_tail(&en1->list, &sbi->extent_list);
> > + if (en2 && en2->ei.len >= F2FS_MIN_EXTENT_LEN)
> > + list_add_tail(&en2->list, &sbi->extent_list);
> > + if (en3) {
> > + if (list_empty(&en3->list))
> > + list_add_tail(&en3->list, &sbi->extent_list);
> > + else
> > + list_move_tail(&en3->list, &sbi->extent_list);
> > + }
> > + if (den && !list_empty(&den->list))
> > + list_del_init(&den->list);
> > + spin_unlock(&sbi->extent_lock);
> > +
> > + if (en) {
> > + kmem_cache_free(extent_node_slab, en);
> > + atomic_dec(&sbi->total_ext_node);
>
> --> move into __detach_extent_node().
will do.
>
> > + }
> > + if (den) {
> > + kmem_cache_free(extent_node_slab, den);
> > + atomic_dec(&sbi->total_ext_node);
> > + }
> > +
> > + write_unlock(&et->lock);
> > + atomic_dec(&et->refcount);
> > +}
> > +
> > +void f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
> > +{
> > + struct extent_tree *treevec[EXT_TREE_VEC_SIZE];
> > + struct extent_node *en, *tmp;
> > + unsigned long ino = F2FS_ROOT_INO(sbi);
> > + struct radix_tree_iter iter;
> > + void **slot;
> > + unsigned int found;
> > + unsigned int node_cnt = 0, tree_cnt = 0;
> > +
> > + if (available_free_memory(sbi, EXTENT_CACHE))
> > + return;
> > +
> > + spin_lock(&sbi->extent_lock);
> > + list_for_each_entry_safe(en, tmp, &sbi->extent_list, list) {
> > + if (!nr_shrink--)
> > + break;
> > + list_del_init(&en->list);
> > + }
> > + spin_unlock(&sbi->extent_lock);
> > +
> > + down_read(&sbi->extent_tree_lock);
> > + while ((found = radix_tree_gang_lookup(&sbi->extent_tree_root,
> > + (void **)treevec, ino, EXT_TREE_VEC_SIZE))) {
> > + unsigned i;
> > +
> > + ino = treevec[found - 1]->ino + 1;
> > + for (i = 0; i < found; i++) {
> > + struct extent_tree *et = treevec[i];
> > +
> > + atomic_inc(&et->refcount);
> > + write_lock(&et->lock);
> > + node_cnt += __free_extent_tree(sbi, et, false);
> > + write_unlock(&et->lock);
> > + atomic_dec(&et->refcount);
> > + }
> > + }
> > + up_read(&sbi->extent_tree_lock);
> > +
> > + down_write(&sbi->extent_tree_lock);
> > + radix_tree_for_each_slot(slot, &sbi->extent_tree_root, &iter,
> > + F2FS_ROOT_INO(sbi)) {
> > + struct extent_tree *et = (struct extent_tree *)*slot;
> > +
> > + if (!atomic_read(&et->refcount) && !et->count) {
> > + radix_tree_delete(&sbi->extent_tree_root, et->ino);
> > + kmem_cache_free(extent_tree_slab, et);
> > + sbi->total_ext_tree--;
> > + tree_cnt++;
>
> No use of tree_cnt.
This is used by trace function in RFC PATCH 10/10.
Thanks for your review! :)
Regards,
Yu
>
> Thanks,
[snip]
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