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Date: Mon, 17 Mar 2014 16:07:12 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: tytso@....edu, linux-ext4@...r.kernel.org,
Andreas Dilger <andreas.dilger@...el.com>
Subject: Re: [PATCH 35/49] ext2fs: add readahead method to improve scanning
On Mar 11, 2014, at 12:57 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> Frøm: Andreas Dilger <adilger@...mcloud.com>
>
> Add a readahead method for prefetching ranges of disk blocks. This is
> useful for inode table scanning, and other large contiguous ranges of
> blocks, and may also prove useful for random block prefetch, since it
> will allow reordering of the IO without waiting synchronously for the
> reads to complete.
>
> It is currently using the posix_fadvise(POSIX_FADV_WILLNEED)
> interface, as this proved most efficient during our testing.
>
> [darrick.wong@...cle.com]
> Add a cache_release method for advising the pagecache to discard disk
> cache blocks. Make the arguments to the readahead function take the
> same ULL values as the other IO functions, and return an appropriate
> error code when fadvise isn't available.
This already has my Signed-off-by: line, but I thought I'd chime in that
I also reviewed the later additions from Darrick for the cache release.
Cheers, Andreas
> Signed-off-by: Andreas Dilger <andreas.dilger@...el.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
> lib/ext2fs/ext2_io.h | 12 ++++++++++++
> lib/ext2fs/io_manager.c | 18 ++++++++++++++++++
> lib/ext2fs/unix_io.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
> 3 files changed, 73 insertions(+), 3 deletions(-)
>
>
> diff --git a/lib/ext2fs/ext2_io.h b/lib/ext2fs/ext2_io.h
> index 1894fb8..636f797 100644
> --- a/lib/ext2fs/ext2_io.h
> +++ b/lib/ext2fs/ext2_io.h
> @@ -90,6 +90,12 @@ struct struct_io_manager {
> int count, const void *data);
> errcode_t (*discard)(io_channel channel, unsigned long long block,
> unsigned long long count);
> + errcode_t (*cache_readahead)(io_channel channel,
> + unsigned long long block,
> + unsigned long long count);
> + errcode_t (*cache_release)(io_channel channel,
> + unsigned long long block,
> + unsigned long long count);
> long reserved[16];
> };
>
> @@ -124,6 +130,12 @@ extern errcode_t io_channel_discard(io_channel channel,
> unsigned long long count);
> extern errcode_t io_channel_alloc_buf(io_channel channel,
> int count, void *ptr);
> +extern errcode_t io_channel_cache_readahead(io_channel io,
> + unsigned long long block,
> + unsigned long long count);
> +extern errcode_t io_channel_cache_release(io_channel io,
> + unsigned long long block,
> + unsigned long long count);
>
> /* unix_io.c */
> extern io_manager unix_io_manager;
> diff --git a/lib/ext2fs/io_manager.c b/lib/ext2fs/io_manager.c
> index 34e4859..a1258c4 100644
> --- a/lib/ext2fs/io_manager.c
> +++ b/lib/ext2fs/io_manager.c
> @@ -128,3 +128,21 @@ errcode_t io_channel_alloc_buf(io_channel io, int count, void *ptr)
> else
> return ext2fs_get_mem(size, ptr);
> }
> +
> +errcode_t io_channel_cache_readahead(io_channel io, unsigned long long block,
> + unsigned long long count)
> +{
> + if (!io->manager->cache_readahead)
> + return EXT2_ET_OP_NOT_SUPPORTED;
> +
> + return io->manager->cache_readahead(io, block, count);
> +}
> +
> +errcode_t io_channel_cache_release(io_channel io, unsigned long long block,
> + unsigned long long count)
> +{
> + if (!io->manager->cache_release)
> + return EXT2_ET_OP_NOT_SUPPORTED;
> +
> + return io->manager->cache_release(io, block, count);
> +}
> diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
> index a818c13..a95e289 100644
> --- a/lib/ext2fs/unix_io.c
> +++ b/lib/ext2fs/unix_io.c
> @@ -15,6 +15,9 @@
> * %End-Header%
> */
>
> +#define _XOPEN_SOURCE 600
> +#define _DARWIN_C_SOURCE
> +#define _FILE_OFFSET_BITS 64
> #define _LARGEFILE_SOURCE
> #define _LARGEFILE64_SOURCE
> #ifndef _GNU_SOURCE
> @@ -35,6 +38,9 @@
> #ifdef __linux__
> #include <sys/utsname.h>
> #endif
> +#if HAVE_SYS_TYPES_H
> +#include <sys/types.h>
> +#endif
> #ifdef HAVE_SYS_IOCTL_H
> #include <sys/ioctl.h>
> #endif
> @@ -44,9 +50,6 @@
> #if HAVE_SYS_STAT_H
> #include <sys/stat.h>
> #endif
> -#if HAVE_SYS_TYPES_H
> -#include <sys/types.h>
> -#endif
> #if HAVE_SYS_RESOURCE_H
> #include <sys/resource.h>
> #endif
> @@ -97,6 +100,7 @@ struct unix_private_data {
> #define IS_ALIGNED(n, align) ((((unsigned long) n) & \
> ((unsigned long) ((align)-1))) == 0)
>
> +
> static errcode_t unix_get_stats(io_channel channel, io_stats *stats)
> {
> errcode_t retval = 0;
> @@ -810,6 +814,40 @@ static errcode_t unix_write_blk64(io_channel channel, unsigned long long block,
> #endif /* NO_IO_CACHE */
> }
>
> +static errcode_t unix_cache_readahead(io_channel channel,
> + unsigned long long block,
> + unsigned long long count)
> +{
> +#ifdef POSIX_FADV_WILLNEED
> + struct unix_private_data *data;
> +
> + data = (struct unix_private_data *)channel->private_data;
> + return posix_fadvise(data->dev,
> + (ext2_loff_t)block * channel->block_size,
> + (ext2_loff_t)count * channel->block_size,
> + POSIX_FADV_WILLNEED);
> +#else
> + return EXT2_ET_OP_NOT_SUPPORTED;
> +#endif
> +}
> +
> +static errcode_t unix_cache_release(io_channel channel,
> + unsigned long long block,
> + unsigned long long count)
> +{
> +#ifdef POSIX_FADV_DONTNEED
> + struct unix_private_data *data;
> +
> + data = (struct unix_private_data *)channel->private_data;
> + return posix_fadvise(data->dev,
> + (ext2_loff_t)block * channel->block_size,
> + (ext2_loff_t)count * channel->block_size,
> + POSIX_FADV_DONTNEED);
> +#else
> + return EXT2_ET_OP_NOT_SUPPORTED;
> +#endif
> +}
> +
> static errcode_t unix_write_blk(io_channel channel, unsigned long block,
> int count, const void *buf)
> {
> @@ -961,6 +999,8 @@ static struct struct_io_manager struct_unix_manager = {
> unix_read_blk64,
> unix_write_blk64,
> unix_discard,
> + unix_cache_readahead,
> + unix_cache_release,
> };
>
> io_manager unix_io_manager = &struct_unix_manager;
>
> --
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Cheers, Andreas
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