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Date: Mon, 3 Feb 2014 14:20:01 -0700
From: Andreas Dilger <adilger@...ger.ca>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: Theodore Ts'o <tytso@....edu>,
linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 3/3] e2fsck: read-ahead metadata during pass1 and pass2
On Feb 1, 2014, at 3:37 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
> index 7554f4e..590e1bd 100644
> --- a/e2fsck/pass1.c
> +++ b/e2fsck/pass1.c
> @@ -574,6 +577,20 @@ static errcode_t recheck_bad_inode_checksum(ext2_filsys fs, ext2_ino_t ino,
> return 0;
> }
>
> +static void *pass1_readahead(void *p)
> +{
> + errcode_t err;
> + e2fsck_t ctx = (e2fsck_t)p;
> +
> + printf("%s: START READAHEAD\n", __func__);
> + err = ext2fs_readahead(ctx->fs, EXT2FS_READ_BBITMAP |
> + EXT2FS_READ_IBITMAP | EXT2FS_READ_ITABLE,
> + 0, ctx->fs->group_desc_count);
This is basically launching readahead for the whole filesystem in one
shot. That might be OK for small filesystems or running a single large
filesystem on a big machine, but could cause memory pressure and cache
eviction for many/large filesystems.
Have you done any tests to see what a limited readahead would do for
performance (say 8-16 groups ahead)?
Also, the bitmaps are not needed until pass 5, but would benefit from
being prefetched along with the inode table for non-flex_bg filesystems.
Probably there is little to no benefit to prefetching them in pass1 for
flex_bg filesystems.
Cheers, Andreas
> + printf("%s: READAHEAD=%d\n", __func__, (int)err);
> +
> + return NULL;
> +}
> +
> void e2fsck_pass1(e2fsck_t ctx)
> {
> int i;
> @@ -600,6 +617,15 @@ void e2fsck_pass1(e2fsck_t ctx)
> init_resource_track(&rtrack, ctx->fs->io);
> clear_problem_context(&pctx);
>
> + if (getenv("READAHEAD")) {
> +#ifdef HAVE_PTHREAD_H
> + pthread_t tid;
> + pthread_create(&tid, NULL, pass1_readahead, ctx);
> +#else
> + pass1_readahead(ctx);
> +#endif
> + }
> +
> if (!(ctx->options & E2F_OPT_PREEN))
> fix_problem(ctx, PR_1_PASS_HEADER, &pctx);
>
> diff --git a/e2fsck/pass2.c b/e2fsck/pass2.c
> index 5a2745a..bd7323f 100644
> --- a/e2fsck/pass2.c
> +++ b/e2fsck/pass2.c
> @@ -44,6 +44,9 @@
> #define _GNU_SOURCE 1 /* get strnlen() */
> #include "config.h"
> #include <string.h>
> +#ifdef HAVE_PTHREAD_H
> +#include <pthread.h>
> +#endif
>
> #include "e2fsck.h"
> #include "problem.h"
> @@ -79,6 +82,29 @@ struct check_dir_struct {
> e2fsck_t ctx;
> };
>
> +struct pass2_readahead_data {
> + ext2_filsys fs;
> + ext2_dblist dblist;
> +};
> +
> +static int readahead_dir_block(ext2_filsys fs, struct ext2_db_entry2 *db,
> + void *priv_data)
> +{
> + db->blockcnt = 1;
> +}
> +
> +static void *pass2_readahead(void *p)
> +{
> + errcode_t err;
> + struct pass2_readahead_data *pr = p;
> +
> + printf("%s: START READAHEAD\n", __func__);
> + err = ext2fs_readahead_dblist(pr->fs, pr->dblist);
> + ext2fs_free_dblist(pr->dblist);
> + ext2fs_free_mem(&pr);
> + printf("%s: END READAHEAD %d\n", __func__, (int)err);
> +}
> +
> void e2fsck_pass2(e2fsck_t ctx)
> {
> struct ext2_super_block *sb = ctx->fs->super;
> @@ -146,6 +172,41 @@ void e2fsck_pass2(e2fsck_t ctx)
> if (fs->super->s_feature_compat & EXT2_FEATURE_COMPAT_DIR_INDEX)
> ext2fs_dblist_sort2(fs->dblist, special_dir_block_cmp);
>
> + if (getenv("READAHEAD")) {
> +#ifdef HAVE_PTHREAD_H
> + pthread_t tid;
> +#endif
> + struct pass2_readahead_data *pr;
> + errcode_t err;
> +
> + err = ext2fs_get_mem(sizeof(*pr), &pr);
> + if (err)
> + goto no_readahead;
> + pr->fs = fs;
> + err = ext2fs_copy_dblist(fs->dblist, &pr->dblist);
> + if (err) {
> + ext2fs_free_mem(&pr);
> + goto no_readahead;
> + }
> + err = ext2fs_dblist_iterate2(pr->dblist, readahead_dir_block,
> + NULL);
> + if (err) {
> + ext2fs_free_dblist(pr->dblist);
> + ext2fs_free_mem(&pr);
> + goto no_readahead;
> + }
> +#ifdef HAVE_PTHREAD_H
> + err = pthread_create(&tid, NULL, pass2_readahead, pr);
> +#else
> + pass2_readahead(pr);
> +#endif
> + if (err) {
> + ext2fs_free_dblist(pr->dblist);
> + ext2fs_free_mem(&pr);
> + }
> + }
> +
> +no_readahead:
> cd.pctx.errcode = ext2fs_dblist_iterate2(fs->dblist, check_dir_block,
> &cd);
> if (ctx->flags & E2F_FLAG_SIGNAL_MASK || ctx->flags & E2F_FLAG_RESTART)
> diff --git a/lib/config.h.in b/lib/config.h.in
> index 35ece01..1dd33b4 100644
> --- a/lib/config.h.in
> +++ b/lib/config.h.in
> @@ -206,6 +206,9 @@
> /* Define if your <locale.h> file defines LC_MESSAGES. */
> #undef HAVE_LC_MESSAGES
>
> +/* Define to 1 if you have the `pthread' library (-lpthread). */
> +#undef HAVE_LIBPTHREAD
> +
> /* Define to 1 if you have the <limits.h> header file. */
> #undef HAVE_LIMITS_H
>
> @@ -314,6 +317,9 @@
> /* Define to 1 if you have the `prctl' function. */
> #undef HAVE_PRCTL
>
> +/* Define to 1 if you have the <pthread.h> header file. */
> +#undef HAVE_PTHREAD_H
> +
> /* Define to 1 if you have the `putenv' function. */
> #undef HAVE_PUTENV
>
>
> --
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Cheers, Andreas
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