RE: [RFC PATCH 1/1] ext4: Try to better reuse recently freed space

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Thank you very much for looking into this issue Lukas!

Ric,
What are the odds of getting a patch as a hot fix or beta for a proof of concept?
The deadline is 7/15/2013 and this may eliminate the biggest remaining issue.

Thanks again and best regards,

Mario

> -----Original Message-----
> From: Lukáš Czerner [mailto:lczerner@xxxxxxxxxx]
> Sent: Thursday, July 04, 2013 10:33 AM
> To: Jan Kara
> Cc: linux-ext4@xxxxxxxxxxxxxxx; enwlinux@xxxxxxxxx; Gallegos, Mario;
> Hargrave, Jordan; rwheeler@xxxxxxxxxx
> Subject: Re: [RFC PATCH 1/1] ext4: Try to better reuse recently freed space
> 
> On Thu, 4 Jul 2013, Jan Kara wrote:
> 
> > Date: Thu, 4 Jul 2013 17:09:05 +0200
> > From: Jan Kara <jack@xxxxxxx>
> > To: Lukas Czerner <lczerner@xxxxxxxxxx>
> > Cc: linux-ext4@xxxxxxxxxxxxxxx, enwlinux@xxxxxxxxx,
> >     Jose_Mario_Gallegos@xxxxxxxx, jordan_hargrave@xxxxxxxx,
> >     rwheeler@xxxxxxxxxx
> > Subject: Re: [RFC PATCH 1/1] ext4: Try to better reuse recently freed
> > space
> >
> > On Thu 04-07-13 11:11:54, Lukas Czerner wrote:
> > > Currently if the block allocator can not find the goal to allocate
> > > we would use global goal for stream allocation. However the global
> > > goal (s_mb_last_group and s_mb_last_start) will move further every
> > > time such allocation appears and never move backwards.
> > >
> > > This causes several problems in certain scenarios:
> > >
> > > - the goal will move further and further preventing us from reusing
> > >   space which might have been freed since then. This is ok from the file
> > >   system point of view because we will reuse that space eventually,
> > >   however we're allocating block from slower parts of the spinning disk
> > >   even though it might not be necessary.
> > > - The above also causes more serious problem for example for thinly
> > >   provisioned storage (sparse images backed storage as well), because
> > >   instead of reusing blocks which are already provisioned we would try
> > >   to use new blocks. This would unnecessarily drain storage free blocks
> > >   pool.
> > > - This will also cause blocks to be allocated further from the given
> > >   goal than it's necessary. Consider for example truncating, or removing
> > >   and rewriting the file in the loop. This workload will never reuse
> > >   freed blocks until we continually claim and free all the block in the
> > >   file system.
> > >
> > > Note that file systems like xfs, ext3, or btrfs does not have this
> > > problem. This is simply caused by the notion of global pool.
> > >
> > > Fix this by changing the global goal to be goal per inode. This will
> > > allow us to invalidate the goal every time the inode has been
> > > truncated, or newly created, so in those cases we would try to use
> > > the proper more specific goal which is based on inode position.
> >   In principle the patch looks fine to me. Just minor style nit below:
> >
> > >
> > > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> > > ---
> > >  fs/ext4/ext4.h    |  7 ++++---
> > >  fs/ext4/inode.c   |  8 ++++++++
> > >  fs/ext4/mballoc.c | 20 ++++++++------------
> > >  3 files changed, 20 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 6ed348d..4dffa92
> > > 100644
> > > --- a/fs/ext4/ext4.h
> > > +++ b/fs/ext4/ext4.h
> > > @@ -917,6 +917,10 @@ struct ext4_inode_info {
> > >
> > >  	/* Precomputed uuid+inum+igen checksum for seeding inode
> checksums */
> > >  	__u32 i_csum_seed;
> > > +
> > > +	/* where last allocation was done - for stream allocation */
> > > +	unsigned long i_last_group;
> > > +	unsigned long i_last_start;
> >   Can we use proper types here please? I think they should be
> > ext4_grpblk_t and ext4_group_t. And maybe we should define something
> > like EXT4_INVAL_GRPNO and use that instead of UINT_MAX.
> 
> Sure, it'll look better with named types and defined invalidate value. I'll
> resend the patch soon.
> 
> Thanks!
> -Lukas
> 
> >
> > 								Honza
> > >  };
> > >
> > >  /*
> > > @@ -1242,9 +1246,6 @@ struct ext4_sb_info {
> > >  	unsigned int s_mb_order2_reqs;
> > >  	unsigned int s_mb_group_prealloc;
> > >  	unsigned int s_max_dir_size_kb;
> > > -	/* where last allocation was done - for stream allocation */
> > > -	unsigned long s_mb_last_group;
> > > -	unsigned long s_mb_last_start;
> > >
> > >  	/* stats for buddy allocator */
> > >  	atomic_t s_bal_reqs;	/* number of reqs with len > 1 */
> > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index
> > > 0188e65..07d0434 100644
> > > --- a/fs/ext4/inode.c
> > > +++ b/fs/ext4/inode.c
> > > @@ -3702,6 +3702,10 @@ void ext4_truncate(struct inode *inode)
> > >  	else
> > >  		ext4_ind_truncate(handle, inode);
> > >
> > > +	/* Invalidate last allocation counters */
> > > +	ei->i_last_group = UINT_MAX;
> > > +	ei->i_last_start = UINT_MAX;
> > > +
> >   And
> > >  	up_write(&ei->i_data_sem);
> > >
> > >  	if (IS_SYNC(inode))
> > > @@ -4060,6 +4064,10 @@ struct inode *ext4_iget(struct super_block
> *sb, unsigned long ino)
> > >  	inode->i_generation = le32_to_cpu(raw_inode->i_generation);
> > >  	ei->i_block_group = iloc.block_group;
> > >  	ei->i_last_alloc_group = ~0;
> > > +
> > > +	/* Invalidate last allocation counters */
> > > +	ei->i_last_group = UINT_MAX;
> > > +	ei->i_last_start = UINT_MAX;
> > >  	/*
> > >  	 * NOTE! The in-memory inode i_data array is in little-endian order
> > >  	 * even on big-endian machines: we do NOT byteswap the block
> numbers!
> > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index
> > > a9ff5e5..6c23666 100644
> > > --- a/fs/ext4/mballoc.c
> > > +++ b/fs/ext4/mballoc.c
> > > @@ -1591,7 +1591,6 @@ static int mb_mark_used(struct ext4_buddy
> > > *e4b, struct ext4_free_extent *ex)  static void
> ext4_mb_use_best_found(struct ext4_allocation_context *ac,
> > >  					struct ext4_buddy *e4b)
> > >  {
> > > -	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> > >  	int ret;
> > >
> > >  	BUG_ON(ac->ac_b_ex.fe_group != e4b->bd_group); @@ -1622,10
> +1621,8
> > > @@ static void ext4_mb_use_best_found(struct
> ext4_allocation_context *ac,
> > >  	get_page(ac->ac_buddy_page);
> > >  	/* store last allocated for subsequent stream allocation */
> > >  	if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
> > > -		spin_lock(&sbi->s_md_lock);
> > > -		sbi->s_mb_last_group = ac->ac_f_ex.fe_group;
> > > -		sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
> > > -		spin_unlock(&sbi->s_md_lock);
> > > +		EXT4_I(ac->ac_inode)->i_last_group = ac-
> >ac_f_ex.fe_group;
> > > +		EXT4_I(ac->ac_inode)->i_last_start = ac->ac_f_ex.fe_start;
> > >  	}
> > >  }
> > >
> > > @@ -2080,13 +2077,12 @@ ext4_mb_regular_allocator(struct
> ext4_allocation_context *ac)
> > >  			ac->ac_2order = i - 1;
> > >  	}
> > >
> > > -	/* if stream allocation is enabled, use global goal */
> > > -	if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
> > > -		/* TBD: may be hot point */
> > > -		spin_lock(&sbi->s_md_lock);
> > > -		ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
> > > -		ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
> > > -		spin_unlock(&sbi->s_md_lock);
> > > +	/* if stream allocation is enabled and per inode goal is
> > > +	 * set, use it */
> > > +	if ((ac->ac_flags & EXT4_MB_STREAM_ALLOC) &&
> > > +	   (EXT4_I(ac->ac_inode)->i_last_start != UINT_MAX)) {
> > > +		ac->ac_g_ex.fe_group = EXT4_I(ac->ac_inode)-
> >i_last_group;
> > > +		ac->ac_g_ex.fe_start = EXT4_I(ac->ac_inode)->i_last_start;
> > >  	}
> > >
> > >  	/* Let's just scan groups to find more-less suitable blocks */
> > > --
> > > 1.8.3.1
> > >
> > > --
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