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Date:   Fri, 19 Jun 2020 00:27:42 +0900
From:   Wang Shilong <wangshilong1991@...il.com>
To:     linux-ext4@...r.kernel.org
Cc:     lixi@....com, adilger@...ger.ca, wangshilong1991@...il.com,
        sihara@....com, Wang Shilong <wshilong@....com>
Subject: [RFC PATCH v2 39/51] e2fsck: fix readahead for pfsck of pass1

From: Wang Shilong <wshilong@....com>

Several improvments for this patch:

1) move readahead_kb detection to preparing phase.
2) inode readahead should be aware of thread block group
boundary.
3) make readahead_kb aware of multiple threads.

Signed-off-by: Wang Shilong <wshilong@....com>
---
 e2fsck/pass1.c | 90 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 55 insertions(+), 35 deletions(-)

diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
index 0cc4e60d..457c713f 100644
--- a/e2fsck/pass1.c
+++ b/e2fsck/pass1.c
@@ -1177,13 +1177,14 @@ static void pass1_readahead(e2fsck_t ctx, dgrp_t *group, ext2_ino_t *next_ino)
 	dgrp_t start = *group, grp;
 	blk64_t blocks_to_read = 0;
 	errcode_t err = EXT2_ET_INVALID_ARGUMENT;
+	dgrp_t grp_end = ctx->thread_info.et_group_end;
 
 	if (ctx->readahead_kb == 0)
 		goto out;
 
 	/* Keep iterating groups until we have enough to readahead */
 	inodes_per_block = EXT2_INODES_PER_BLOCK(ctx->fs->super);
-	for (grp = start; grp < ctx->fs->group_desc_count; grp++) {
+	for (grp = start; grp < grp_end; grp++) {
 		if (ext2fs_bg_flags_test(ctx->fs, grp, EXT2_BG_INODE_UNINIT))
 			continue;
 		inodes_in_group = ctx->fs->super->s_inodes_per_group -
@@ -1275,6 +1276,38 @@ static int e2fsck_should_abort(e2fsck_t ctx)
 	return 0;
 }
 
+/**
+ * Even though we could specify number of threads,
+ * but it might be more than the whole filesystem
+ * block groups, correct it here.
+ */
+static void e2fsck_pass1_set_thread_num(e2fsck_t ctx)
+{
+	unsigned flexbg_size = 1;
+	ext2_filsys fs = ctx->fs;
+	int num_threads = ctx->fs_num_threads;
+	int max_threads;
+
+	if (num_threads < 1)
+		num_threads = 1;
+
+	if (ext2fs_has_feature_flex_bg(fs->super))
+		flexbg_size = 1 << fs->super->s_log_groups_per_flex;
+
+	max_threads = fs->group_desc_count / flexbg_size;
+	if (max_threads == 0)
+		num_threads = 1;
+	else if (max_threads % num_threads) {
+		int times = max_threads / num_threads;
+
+		if (times == 0)
+			num_threads = max_threads;
+		else
+			num_threads = max_threads / times;
+	}
+	ctx->fs_num_threads = num_threads;
+}
+
 /*
  * We need call mark_table_blocks() before multiple
  * thread start, since all known system blocks should be
@@ -1284,6 +1317,20 @@ static int _e2fsck_pass1_prepare(e2fsck_t ctx)
 {
 	struct problem_context pctx;
 	ext2_filsys fs = ctx->fs;
+	unsigned long long readahead_kb;
+
+	e2fsck_pass1_set_thread_num(ctx);
+	/* If we can do readahead, figure out how many groups to pull in. */
+	if (!e2fsck_can_readahead(ctx->fs))
+		ctx->readahead_kb = 0;
+	else if (ctx->readahead_kb == ~0ULL)
+		ctx->readahead_kb = e2fsck_guess_readahead(ctx->fs);
+
+	/* don't use more than 1/10 of memory for threads checking */
+	readahead_kb = get_memory_size() / (10 * ctx->fs_num_threads);
+	/* maybe better disable RA if this is too small? */
+	if (ctx->readahead_kb > readahead_kb)
+		ctx->readahead_kb = readahead_kb;
 
 	clear_problem_context(&pctx);
 	if (!(ctx->options & E2F_OPT_PREEN))
@@ -1467,13 +1514,7 @@ void _e2fsck_pass1(e2fsck_t ctx)
 	init_resource_track(&rtrack, ctx->fs->io);
 	clear_problem_context(&pctx);
 
-	/* If we can do readahead, figure out how many groups to pull in. */
-	if (!e2fsck_can_readahead(ctx->fs))
-		ctx->readahead_kb = 0;
-	else if (ctx->readahead_kb == ~0ULL)
-		ctx->readahead_kb = e2fsck_guess_readahead(ctx->fs);
 	pass1_readahead(ctx, &ra_group, &ino_threshold);
-
 	if (ext2fs_has_feature_dir_index(fs->super) &&
 	    !(ctx->options & E2F_OPT_NO)) {
 		if (ext2fs_u32_list_create(&ctx->dirs_to_hash, 50))
@@ -2997,7 +3038,7 @@ static int e2fsck_pass1_thread_join(e2fsck_t global_ctx, e2fsck_t thread_ctx)
 }
 
 static int e2fsck_pass1_threads_join(struct e2fsck_thread_info *infos,
-				      int num_threads, e2fsck_t global_ctx)
+				     e2fsck_t global_ctx)
 {
 	errcode_t			 rc;
 	errcode_t			 ret = 0;
@@ -3006,7 +3047,7 @@ static int e2fsck_pass1_threads_join(struct e2fsck_thread_info *infos,
 
 	/* merge invalid bitmaps will recalculate it */
 	global_ctx->invalid_bitmaps = 0;
-	for (i = 0; i < num_threads; i++) {
+	for (i = 0; i < global_ctx->fs_num_threads; i++) {
 		pinfo = &infos[i];
 
 		if (!pinfo->eti_started)
@@ -3083,7 +3124,7 @@ out:
 }
 
 static int e2fsck_pass1_threads_start(struct e2fsck_thread_info **pinfo,
-				      int num_threads, e2fsck_t global_ctx)
+				      e2fsck_t global_ctx)
 {
 	struct e2fsck_thread_info	*infos;
 	pthread_attr_t			 attr;
@@ -3098,6 +3139,7 @@ static int e2fsck_pass1_threads_start(struct e2fsck_thread_info **pinfo,
 
 	thread_debug.etd_finished_threads = 0;
 #endif
+	int num_threads = global_ctx->fs_num_threads;
 
 	retval = pthread_attr_init(&attr);
 	if (retval) {
@@ -3152,7 +3194,7 @@ static int e2fsck_pass1_threads_start(struct e2fsck_thread_info **pinfo,
 	}
 
 	if (retval) {
-		e2fsck_pass1_threads_join(infos, num_threads, global_ctx);
+		e2fsck_pass1_threads_join(infos, global_ctx);
 		return retval;
 	}
 	*pinfo = infos;
@@ -3183,13 +3225,7 @@ static void init_ext2_max_sizes()
 static void e2fsck_pass1_multithread(e2fsck_t global_ctx)
 {
 	struct e2fsck_thread_info	*infos = NULL;
-	int num_threads = global_ctx->fs_num_threads;
 	errcode_t			 retval;
-	unsigned flexbg_size = 1;
-	int max_threads;
-
-	if (num_threads < 1)
-		num_threads = 1;
 
 	retval = _e2fsck_pass1_prepare(global_ctx);
 	if (retval)
@@ -3198,31 +3234,15 @@ static void e2fsck_pass1_multithread(e2fsck_t global_ctx)
 	pthread_mutex_init(&global_ctx->fs_fix_mutex, NULL);
 	pthread_rwlock_init(&global_ctx->fs_block_map_rwlock, NULL);
 	pthread_mutex_init(&global_ctx->fs_ea_mutex, NULL);
-	if (ext2fs_has_feature_flex_bg(global_ctx->fs->super))
-		flexbg_size = 1 << global_ctx->fs->super->s_log_groups_per_flex;
-
-	max_threads = global_ctx->fs->group_desc_count / flexbg_size;
-	if (max_threads == 0)
-		num_threads = 1;
-	else if (max_threads % num_threads) {
-		int times = max_threads / num_threads;
-
-		if (times == 0)
-			num_threads = max_threads;
-		else
-			num_threads = max_threads / times;
-	}
-
-	global_ctx->fs_num_threads = num_threads;
 	init_ext2_max_sizes();
-	retval = e2fsck_pass1_threads_start(&infos, num_threads, global_ctx);
+	retval = e2fsck_pass1_threads_start(&infos, global_ctx);
 	if (retval) {
 		com_err(global_ctx->program_name, retval,
 			_("while starting pass1 threads\n"));
 		goto out_abort;
 	}
 
-	retval = e2fsck_pass1_threads_join(infos, num_threads, global_ctx);
+	retval = e2fsck_pass1_threads_join(infos, global_ctx);
 	if (retval) {
 		com_err(global_ctx->program_name, retval,
 			_("while joining pass1 threads\n"));
-- 
2.25.4

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