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Date: Sat, 1 Feb 2014 02:41:03 -0800
From: "Darrick J. Wong" <darrick.wong@...cle.com>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/3] libext2fs: allow clients to read-ahead metadata
On Sat, Feb 01, 2014 at 02:37:35AM -0800, Darrick J. Wong wrote:
> This patch adds to libext2fs the ability to pre-fetch metadata
> into the page cache in the hopes of speeding up libext2fs' clients.
> There are two new library functions -- the first allows a client to
> readahead a list of blocks, and the second is a helper function that
> uses that first mechanism to load group data (bitmaps, inode tables).
>
> e2fsck will employ both of these methods to speed itself up.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
> lib/ext2fs/Makefile.in | 4 +
> lib/ext2fs/ext2fs.h | 10 +++
> lib/ext2fs/io_manager.c | 2 -
> lib/ext2fs/readahead.c | 153 +++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 168 insertions(+), 1 deletion(-)
> create mode 100644 lib/ext2fs/readahead.c
>
>
> diff --git a/lib/ext2fs/Makefile.in b/lib/ext2fs/Makefile.in
> index 92b6ab0..8f98f4b 100644
> --- a/lib/ext2fs/Makefile.in
> +++ b/lib/ext2fs/Makefile.in
> @@ -77,6 +77,7 @@ OBJS= $(DEBUGFS_LIB_OBJS) $(RESIZE_LIB_OBJS) $(E2IMAGE_LIB_OBJS) \
> qcow2.o \
> read_bb.o \
> read_bb_file.o \
> + readahead.o \
> res_gdt.o \
> rw_bitmaps.o \
> swapfs.o \
> @@ -153,6 +154,7 @@ SRCS= ext2_err.c \
> $(srcdir)/qcow2.c \
> $(srcdir)/read_bb.c \
> $(srcdir)/read_bb_file.c \
> + $(srcdir)/readahead.c \
> $(srcdir)/res_gdt.c \
> $(srcdir)/rw_bitmaps.c \
> $(srcdir)/swapfs.c \
> @@ -887,6 +889,8 @@ read_bb_file.o: $(srcdir)/read_bb_file.c $(top_builddir)/lib/config.h \
> $(srcdir)/ext2_fs.h $(srcdir)/ext3_extents.h $(top_srcdir)/lib/et/com_err.h \
> $(srcdir)/ext2_io.h $(top_builddir)/lib/ext2fs/ext2_err.h \
> $(srcdir)/ext2_ext_attr.h $(srcdir)/bitops.h
> +readahead.o: $(srcdir)/readahead.c $(top_builddir)/lib/config.h \
> + $(srcdir)/ext2fs.h $(srcdir)/ext2_fs.h $(top_builddir)/lib/ext2fs/ext2_err.h
> res_gdt.o: $(srcdir)/res_gdt.c $(top_builddir)/lib/config.h \
> $(top_builddir)/lib/dirpaths.h $(srcdir)/ext2_fs.h \
> $(top_builddir)/lib/ext2fs/ext2_types.h $(srcdir)/ext2fs.h \
> diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
> index 069c1b6..1e06791 100644
> --- a/lib/ext2fs/ext2fs.h
> +++ b/lib/ext2fs/ext2fs.h
> @@ -1543,6 +1543,16 @@ extern errcode_t ext2fs_read_bb_FILE(ext2_filsys fs, FILE *f,
> void (*invalid)(ext2_filsys fs,
> blk_t blk));
>
> +/* readahead.c */
> +#define EXT2FS_READ_SUPER 0x01
> +#define EXT2FS_READ_GDT 0x02
> +#define EXT2FS_READ_BBITMAP 0x04
> +#define EXT2FS_READ_IBITMAP 0x08
> +#define EXT2FS_READ_ITABLE 0x10
> +errcode_t ext2fs_readahead(ext2_filsys fs, int flags, dgrp_t start,
> + dgrp_t ngroups);
> +errcode_t ext2fs_readahead_dblist(ext2_filsys fs, ext2_dblist dblist);
> +
> /* res_gdt.c */
> extern errcode_t ext2fs_create_resize_inode(ext2_filsys fs);
>
> diff --git a/lib/ext2fs/io_manager.c b/lib/ext2fs/io_manager.c
> index 1acbb1d..aae0a4b 100644
> --- a/lib/ext2fs/io_manager.c
> +++ b/lib/ext2fs/io_manager.c
> @@ -135,5 +135,5 @@ errcode_t io_channel_readahead(io_channel io, unsigned long long block,
> if (!io->manager->readahead)
> return EXT2_ET_OP_NOT_SUPPORTED;
>
> - return io->manager->readahead(io, block, nblocks);
> + return io->manager->readahead(io, block, count);
> }
Oops, this hunk of course goes in the previous patch.
--D
> diff --git a/lib/ext2fs/readahead.c b/lib/ext2fs/readahead.c
> new file mode 100644
> index 0000000..05f6135
> --- /dev/null
> +++ b/lib/ext2fs/readahead.c
> @@ -0,0 +1,153 @@
> +/*
> + * readahead.c -- Try to convince the OS to prefetch metadata.
> + *
> + * Copyright (C) 2014 Oracle.
> + *
> + * %Begin-Header%
> + * This file may be redistributed under the terms of the GNU Library
> + * General Public License, version 2.
> + * %End-Header%
> + */
> +
> +#include "config.h"
> +#include <string.h>
> +
> +#include "ext2_fs.h"
> +#include "ext2fs.h"
> +
> +struct read_dblist {
> + errcode_t err;
> + blk64_t run_start;
> + blk64_t run_len;
> +};
> +
> +static EXT2_QSORT_TYPE readahead_dir_block_cmp(const void *a, const void *b)
> +{
> + const struct ext2_db_entry2 *db_a =
> + (const struct ext2_db_entry2 *) a;
> + const struct ext2_db_entry2 *db_b =
> + (const struct ext2_db_entry2 *) b;
> +
> + return (int) (db_a->blk - db_b->blk);
> +}
> +
> +static int readahead_dir_block(ext2_filsys fs, struct ext2_db_entry2 *db,
> + void *priv_data)
> +{
> + errcode_t err = 0;
> + struct read_dblist *pr = priv_data;
> +
> + if (!pr->run_len || db->blk != pr->run_start + pr->run_len) {
> + if (pr->run_len)
> + pr->err = io_channel_readahead(fs->io, pr->run_start,
> + pr->run_len);
> + pr->run_start = db->blk;
> + pr->run_len = 0;
> + }
> + pr->run_len += db->blockcnt;
> +
> + return pr->err ? DBLIST_ABORT : 0;
> +}
> +
> +errcode_t ext2fs_readahead_dblist(ext2_filsys fs, ext2_dblist dblist)
> +{
> + errcode_t err;
> + struct read_dblist pr;
> +
> + ext2fs_dblist_sort2(dblist, readahead_dir_block_cmp);
> +
> + memset(&pr, 0, sizeof(pr));
> + err = ext2fs_dblist_iterate2(dblist, readahead_dir_block, &pr);
> + if (pr.err)
> + return pr.err;
> + if (err)
> + return err;
> +
> + if (pr.run_len)
> + err = io_channel_readahead(fs->io, pr.run_start, pr.run_len);
> +
> + return err;
> +}
> +
> +errcode_t ext2fs_readahead(ext2_filsys fs, int flags, dgrp_t start,
> + dgrp_t ngroups)
> +{
> + blk64_t super, old_gdt, new_gdt;
> + blk_t blocks;
> + dgrp_t i;
> + ext2_dblist dblist;
> + dgrp_t end = start + ngroups;
> + errcode_t err = 0;
> +
> + if (end > fs->group_desc_count)
> + end = fs->group_desc_count;
> +
> + if (flags == 0)
> + return 0;
> +
> + err = ext2fs_init_dblist(fs, &dblist);
> + if (err)
> + return err;
> +
> + for (i = start; i < end; i++) {
> + err = ext2fs_super_and_bgd_loc2(fs, i, &super, &old_gdt,
> + &new_gdt, &blocks);
> + if (err)
> + break;
> +
> + if (flags & EXT2FS_READ_SUPER) {
> + err = ext2fs_add_dir_block2(dblist, 0, super, 0);
> + if (err)
> + break;
> + }
> +
> + if (flags & EXT2FS_READ_GDT) {
> + if (old_gdt)
> + err = ext2fs_add_dir_block2(dblist, 0, old_gdt,
> + blocks);
> + else if (new_gdt)
> + err = ext2fs_add_dir_block2(dblist, 0, new_gdt,
> + blocks);
> + else
> + err = 0;
> + if (err)
> + break;
> + }
> +
> + if ((flags & EXT2FS_READ_BBITMAP) &&
> + !ext2fs_bg_flags_test(fs, i, EXT2_BG_BLOCK_UNINIT) &&
> + ext2fs_bg_free_blocks_count(fs, i) <
> + fs->super->s_blocks_per_group) {
> + super = ext2fs_block_bitmap_loc(fs, i);
> + err = ext2fs_add_dir_block2(dblist, 0, super, 1);
> + if (err)
> + break;
> + }
> +
> + if ((flags & EXT2FS_READ_IBITMAP) &&
> + !ext2fs_bg_flags_test(fs, i, EXT2_BG_INODE_UNINIT) &&
> + ext2fs_bg_free_inodes_count(fs, i) <
> + fs->super->s_inodes_per_group) {
> + super = ext2fs_inode_bitmap_loc(fs, i);
> + err = ext2fs_add_dir_block2(dblist, 0, super, 1);
> + if (err)
> + break;
> + }
> +
> + if ((flags & EXT2FS_READ_ITABLE) &&
> + ext2fs_bg_free_inodes_count(fs, i) <
> + fs->super->s_inodes_per_group) {
> + super = ext2fs_inode_table_loc(fs, i);
> + err = ext2fs_add_dir_block2(dblist, 0, super,
> + fs->inode_blocks_per_group);
> + if (err)
> + break;
> + }
> + }
> +
> + if (!err)
> + err = ext2fs_readahead_dblist(fs, dblist);
> +
> + ext2fs_free_dblist(dblist);
> + return err;
> +}
>
> --
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