Re: [PATCH v3] f2fs: fix out-of-free problem caused by atomic write

[Jaegeuk Kim]

On 11/07, Yunlong Song wrote:
> This patch tries its best to collect prefree segments and make it free to be
> used
> in the commit process, or it will use up free segments since prefree
> segments
> can not be used during commit process.
> 
> As for your suggestion, I do consider that in an initial patch which does
> not send
> out, but I am afraid that will lead to long latency if the atomic file is
> large and the
> device is almost full and fragmented.

Why? f2fs_balance_fs() would be fine to return, if target # of segments can
be found from prefree_segments() by checkpoint like what you did. Otherwise,
it needs to call f2fs_gc().

> 
> On 2017/11/7 9:55, Jaegeuk Kim wrote:
> > On 11/06, Yunlong Song wrote:
> > > f2fs_balance_fs only actives once in the commit_inmem_pages, but there
> > > are more than one page to commit, so all the other pages will miss the
> > > check. This will lead to out-of-free problem when commit a very large
> > > file. However, we cannot do f2fs_balance_fs for each inmem page, since
> > > this will break atomicity. As a result, we should collect prefree
> > > segments if needed.
> > > 
> > > Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
> > > ---
> > >   fs/f2fs/f2fs.h    |  1 +
> > >   fs/f2fs/segment.c | 24 +++++++++++++++++++++++-
> > >   2 files changed, 24 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > > index 13a96b8..04ce48f 100644
> > > --- a/fs/f2fs/f2fs.h
> > > +++ b/fs/f2fs/f2fs.h
> > > @@ -610,6 +610,7 @@ struct f2fs_inode_info {
> > >   	struct list_head inmem_pages;	/* inmemory pages managed by f2fs */
> > >   	struct task_struct *inmem_task;	/* store inmemory task */
> > >   	struct mutex inmem_lock;	/* lock for inmemory pages */
> > > +	unsigned long inmem_blocks;	/* inmemory blocks */
> > >   	struct extent_tree *extent_tree;	/* cached extent_tree entry */
> > >   	struct rw_semaphore dio_rwsem[2];/* avoid racing between dio and gc */
> > >   	struct rw_semaphore i_mmap_sem;
> > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > index 46dfbca..b87ede4 100644
> > > --- a/fs/f2fs/segment.c
> > > +++ b/fs/f2fs/segment.c
> > > @@ -210,6 +210,7 @@ void register_inmem_page(struct inode *inode, struct page *page)
> > >   		list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
> > >   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> > >   	inc_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
> > > +	fi->inmem_blocks++;
> > >   	mutex_unlock(&fi->inmem_lock);
> > >   	trace_f2fs_register_inmem_page(page, INMEM);
> > > @@ -221,6 +222,7 @@ static int __revoke_inmem_pages(struct inode *inode,
> > >   	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> > >   	struct inmem_pages *cur, *tmp;
> > >   	int err = 0;
> > > +	struct f2fs_inode_info *fi = F2FS_I(inode);
> > >   	list_for_each_entry_safe(cur, tmp, head, list) {
> > >   		struct page *page = cur->page;
> > > @@ -263,6 +265,7 @@ static int __revoke_inmem_pages(struct inode *inode,
> > >   		list_del(&cur->list);
> > >   		kmem_cache_free(inmem_entry_slab, cur);
> > >   		dec_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
> > > +		fi->inmem_blocks--;
> > >   	}
> > >   	return err;
> > >   }
> > > @@ -302,6 +305,10 @@ void drop_inmem_pages(struct inode *inode)
> > >   	if (!list_empty(&fi->inmem_ilist))
> > >   		list_del_init(&fi->inmem_ilist);
> > >   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> > > +	if (fi->inmem_blocks) {
> > > +		f2fs_bug_on(sbi, 1);
> > > +		fi->inmem_blocks = 0;
> > > +	}
> > >   	mutex_unlock(&fi->inmem_lock);
> > >   	clear_inode_flag(inode, FI_ATOMIC_FILE);
> > > @@ -326,6 +333,7 @@ void drop_inmem_page(struct inode *inode, struct page *page)
> > >   	f2fs_bug_on(sbi, !cur || cur->page != page);
> > >   	list_del(&cur->list);
> > > +	fi->inmem_blocks--;
> > >   	mutex_unlock(&fi->inmem_lock);
> > >   	dec_page_count(sbi, F2FS_INMEM_PAGES);
> > > @@ -410,6 +418,16 @@ int commit_inmem_pages(struct inode *inode)
> > >   	INIT_LIST_HEAD(&revoke_list);
> > >   	f2fs_balance_fs(sbi, true);
> > > +	if (prefree_segments(sbi)
> > > +		&& has_not_enough_free_secs(sbi, 0,
> > > +		fi->inmem_blocks / BLKS_PER_SEC(sbi))) {
> > > +		struct cp_control cpc;
> > > +
> > > +		cpc.reason = __get_cp_reason(sbi);
> > > +		err = write_checkpoint(sbi, &cpc);
> > > +		if (err)
> > > +			goto drop;
> > What do you want to guarantee with this? How about passing target # of segments
> > into f2fs_balance_fs() so that f2fs_gc() could secure wanted free space in a
> > loop?
> > 
> > Thanks,
> > 
> > > +	}
> > >   	f2fs_lock_op(sbi);
> > >   	set_inode_flag(inode, FI_ATOMIC_COMMIT);
> > > @@ -429,7 +447,7 @@ int commit_inmem_pages(struct inode *inode)
> > >   		ret = __revoke_inmem_pages(inode, &revoke_list, false, true);
> > >   		if (ret)
> > >   			err = ret;
> > > -
> > > +drop:
> > >   		/* drop all uncommitted pages */
> > >   		__revoke_inmem_pages(inode, &fi->inmem_pages, true, false);
> > >   	}
> > > @@ -437,6 +455,10 @@ int commit_inmem_pages(struct inode *inode)
> > >   	if (!list_empty(&fi->inmem_ilist))
> > >   		list_del_init(&fi->inmem_ilist);
> > >   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> > > +	if (fi->inmem_blocks) {
> > > +		f2fs_bug_on(sbi, 1);
> > > +		fi->inmem_blocks = 0;
> > > +	}
> > >   	mutex_unlock(&fi->inmem_lock);
> > >   	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
> > > -- 
> > > 1.8.5.2
> > .
> > 
> 
> -- 
> Thanks,
> Yunlong Song
>