Date:	Fri, 5 Apr 2013 11:35:14 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: optimize ext4_end_io memory usage

On Mon 01-04-13 09:17:48, Dmitry Monakhov wrote:
> ext4_end_io->pages array has is used only for buffered writes and usless
> in case of DIO. This patch allow us to save 1K for each DIO request.
  I have actually a more complete solution to this in my patch queue -
there isn't any need to reference pages from io_end after my patches.
Hopefully I'll be able to send things out later today...

								Honza

> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> ---
>  fs/ext4/ext4.h    |    4 ++--
>  fs/ext4/inode.c   |    3 +--
>  fs/ext4/page-io.c |   39 ++++++++++++++++++++++++++++++++-------
>  3 files changed, 35 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 73f3e60..4c803af 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -219,7 +219,7 @@ typedef struct ext4_io_end {
>  	struct kiocb		*iocb;		/* iocb struct for AIO */
>  	int			result;		/* error value for AIO */
>  	int			num_io_pages;   /* for writepages() */
> -	struct ext4_io_page	*pages[MAX_IO_PAGES]; /* for writepages() */
> +	struct ext4_io_page	**pages; 	/* for writepages() */
>  } ext4_io_end_t;
>  
>  struct ext4_io_submit {
> @@ -2622,7 +2622,7 @@ extern void ext4_add_complete_io(ext4_io_end_t *io_end);
>  extern void ext4_exit_pageio(void);
>  extern void ext4_ioend_shutdown(struct inode *);
>  extern void ext4_free_io_end(ext4_io_end_t *io);
> -extern ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags);
> +extern ext4_io_end_t *ext4_init_io_end(struct inode *inode, int directio, gfp_t flags);
>  extern void ext4_end_io_work(struct work_struct *work);
>  extern void ext4_io_submit(struct ext4_io_submit *io);
>  extern int ext4_bio_write_page(struct ext4_io_submit *io,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index f455ac0..840a23e 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3162,12 +3162,11 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
>  	iocb->private = NULL;
>  	ext4_inode_aio_set(inode, NULL);
>  	if (!is_sync_kiocb(iocb)) {
> -		ext4_io_end_t *io_end = ext4_init_io_end(inode, GFP_NOFS);
> +		ext4_io_end_t *io_end = ext4_init_io_end(inode, 1, GFP_NOFS);
>  		if (!io_end) {
>  			ret = -ENOMEM;
>  			goto retake_lock;
>  		}
> -		io_end->flag |= EXT4_IO_END_DIRECT;
>  		iocb->private = io_end;
>  		/*
>  		 * we save the io structure for current async direct
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index 047a6de..1b8ec50 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -29,16 +29,26 @@
>  #include "xattr.h"
>  #include "acl.h"
>  
> -static struct kmem_cache *io_page_cachep, *io_end_cachep;
> +static struct kmem_cache *io_page_cachep, *io_pgvec_cachep, *io_end_cachep;
>  
>  int __init ext4_init_pageio(void)
>  {
>  	io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
>  	if (io_page_cachep == NULL)
>  		return -ENOMEM;
> +
> +	io_pgvec_cachep = kmem_cache_create("ext4_io_pgvec",
> +					    sizeof(struct ext4_io_page*)
> +					    * MAX_IO_PAGES,
> +					    0, (SLAB_RECLAIM_ACCOUNT), NULL);
> +	if (io_pgvec_cachep == NULL) {
> +		kmem_cache_destroy(io_page_cachep);
> +		return -ENOMEM;
> +	}
>  	io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
>  	if (io_end_cachep == NULL) {
>  		kmem_cache_destroy(io_page_cachep);
> +		kmem_cache_destroy(io_pgvec_cachep);
>  		return -ENOMEM;
>  	}
>  	return 0;
> @@ -47,6 +57,7 @@ int __init ext4_init_pageio(void)
>  void ext4_exit_pageio(void)
>  {
>  	kmem_cache_destroy(io_end_cachep);
> +	kmem_cache_destroy(io_pgvec_cachep);
>  	kmem_cache_destroy(io_page_cachep);
>  }
>  
> @@ -83,12 +94,15 @@ void ext4_free_io_end(ext4_io_end_t *io)
>  	BUG_ON(!io);
>  	BUG_ON(!list_empty(&io->list));
>  	BUG_ON(io->flag & EXT4_IO_END_UNWRITTEN);
> +	BUG_ON(io->num_io_pages && !io->pages);
>  
>  	for (i = 0; i < io->num_io_pages; i++)
>  		put_io_page(io->pages[i]);
>  	io->num_io_pages = 0;
>  	if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count))
>  		wake_up_all(ext4_ioend_wq(io->inode));
> +	if (io->pages)
> +		kmem_cache_free(io_pgvec_cachep, io->pages);
>  	kmem_cache_free(io_end_cachep, io);
>  }
>  
> @@ -212,14 +226,25 @@ int ext4_flush_unwritten_io(struct inode *inode)
>  	return ret;
>  }
>  
> -ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
> +ext4_io_end_t *ext4_init_io_end(struct inode *inode, int directio, gfp_t flags)
>  {
>  	ext4_io_end_t *io = kmem_cache_zalloc(io_end_cachep, flags);
> -	if (io) {
> -		atomic_inc(&EXT4_I(inode)->i_ioend_count);
> -		io->inode = inode;
> -		INIT_LIST_HEAD(&io->list);
> +
> +	if (!io)
> +		return NULL;
> +
> +	if (directio) {
> +		io->flag = EXT4_IO_END_DIRECT;
> +	} else {
> +		io->pages = kmem_cache_zalloc(io_pgvec_cachep, flags);
> +		if (!io->pages) {
> +			kmem_cache_free(io_end_cachep, io);
> +			return NULL;
> +		}
>  	}
> +	atomic_inc(&EXT4_I(inode)->i_ioend_count);
> +	io->inode = inode;
> +	INIT_LIST_HEAD(&io->list);
>  	return io;
>  }
>  
> @@ -327,7 +352,7 @@ static int io_submit_init(struct ext4_io_submit *io,
>  	int nvecs = bio_get_nr_vecs(bh->b_bdev);
>  	struct bio *bio;
>  
> -	io_end = ext4_init_io_end(inode, GFP_NOFS);
> +	io_end = ext4_init_io_end(inode, 0, GFP_NOFS);
>  	if (!io_end)
>  		return -ENOMEM;
>  	bio = bio_alloc(GFP_NOIO, min(nvecs, BIO_MAX_PAGES));
> -- 
> 1.7.1
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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