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Date: Sat, 1 Aug 2020 02:57:57 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Theodore Ts'o <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options
On Jul 31, 2020, at 1:08 PM, Theodore Ts'o <tytso@....edu> wrote:
>
> For file systems where we can afford to keep the buddy bitmaps cached,
> we can speed up initial writes to large file systems by starting to
> load the block allocation bitmaps as soon as the file system is
> mounted. This won't work well for _super_ large file systems, or
> memory constrained systems, so we only enable this when it is
> requested via a mount option.
>
> Addresses-Google-Bug: 159488342
> Signed-off-by: Theodore Ts'o <tytso@....edu>
Reviewed-by: Andreas Dilger <adilger@...ger.ca>
> ---
> fs/ext4/ext4.h | 15 +++++++++-
> fs/ext4/mballoc.c | 10 +++----
> fs/ext4/super.c | 59 +++++++++++++++++++++++++++----------
> include/trace/events/ext4.h | 44 +++++++++++++++++++++++++++
> 4 files changed, 105 insertions(+), 23 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 7451662e092a..4df6f429de1a 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1172,6 +1172,7 @@ struct ext4_inode_info {
> #define EXT4_MOUNT_JOURNAL_CHECKSUM 0x800000 /* Journal checksums */
> #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x1000000 /* Journal Async Commit */
> #define EXT4_MOUNT_WARN_ON_ERROR 0x2000000 /* Trigger WARN_ON on error */
> +#define EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS 0x4000000
> #define EXT4_MOUNT_DELALLOC 0x8000000 /* Delalloc support */
> #define EXT4_MOUNT_DATA_ERR_ABORT 0x10000000 /* Abort on file data write */
> #define EXT4_MOUNT_BLOCK_VALIDITY 0x20000000 /* Block validity checking */
> @@ -2315,9 +2316,15 @@ struct ext4_lazy_init {
> struct mutex li_list_mtx;
> };
>
> +enum ext4_li_mode {
> + EXT4_LI_MODE_PREFETCH_BBITMAP,
> + EXT4_LI_MODE_ITABLE,
> +};
> +
> struct ext4_li_request {
> struct super_block *lr_super;
> - struct ext4_sb_info *lr_sbi;
> + enum ext4_li_mode lr_mode;
> + ext4_group_t lr_first_not_zeroed;
> ext4_group_t lr_next_group;
> struct list_head lr_request;
> unsigned long lr_next_sched;
> @@ -2657,6 +2664,12 @@ extern int ext4_mb_reserve_blocks(struct super_block *, int);
> extern void ext4_discard_preallocations(struct inode *);
> extern int __init ext4_init_mballoc(void);
> extern void ext4_exit_mballoc(void);
> +extern ext4_group_t ext4_mb_prefetch(struct super_block *sb,
> + ext4_group_t group,
> + unsigned int nr, int *cnt);
> +extern void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
> + unsigned int nr);
> +
> extern void ext4_free_blocks(handle_t *handle, struct inode *inode,
> struct buffer_head *bh, ext4_fsblk_t block,
> unsigned long count, int flags);
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index b1ef35a9e9f1..47de61e44db2 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2233,9 +2233,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
> * Start prefetching @nr block bitmaps starting at @group.
> * Return the next group which needs to be prefetched.
> */
> -static ext4_group_t
> -ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
> - unsigned int nr, int *cnt)
> +ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
> + unsigned int nr, int *cnt)
> {
> ext4_group_t ngroups = ext4_get_groups_count(sb);
> struct buffer_head *bh;
> @@ -2285,9 +2284,8 @@ ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
> * waiting for the block allocation bitmap read to finish when
> * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator().
> */
> -static void
> -ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
> - unsigned int nr)
> +void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
> + unsigned int nr)
> {
> while (nr-- > 0) {
> struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group,
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 330957ed1f05..51e91a220ea9 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1521,6 +1521,7 @@ enum {
> Opt_dioread_nolock, Opt_dioread_lock,
> Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
> Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
> + Opt_prefetch_block_bitmaps,
> };
>
> static const match_table_t tokens = {
> @@ -1612,6 +1613,7 @@ static const match_table_t tokens = {
> {Opt_test_dummy_encryption, "test_dummy_encryption"},
> {Opt_nombcache, "nombcache"},
> {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */
> + {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
> {Opt_removed, "check=none"}, /* mount option from ext2/3 */
> {Opt_removed, "nocheck"}, /* mount option from ext2/3 */
> {Opt_removed, "reservation"}, /* mount option from ext2/3 */
> @@ -1829,6 +1831,8 @@ static const struct mount_opts {
> {Opt_max_dir_size_kb, 0, MOPT_GTE0},
> {Opt_test_dummy_encryption, 0, MOPT_STRING},
> {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
> + {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
> + MOPT_SET},
> {Opt_err, 0, 0}
> };
>
> @@ -3201,15 +3205,34 @@ static void print_daily_error_info(struct timer_list *t)
> static int ext4_run_li_request(struct ext4_li_request *elr)
> {
> struct ext4_group_desc *gdp = NULL;
> - ext4_group_t group, ngroups;
> - struct super_block *sb;
> + struct super_block *sb = elr->lr_super;
> + ext4_group_t ngroups = EXT4_SB(sb)->s_groups_count;
> + ext4_group_t group = elr->lr_next_group;
> unsigned long timeout = 0;
> + unsigned int prefetch_ios = 0;
> int ret = 0;
>
> - sb = elr->lr_super;
> - ngroups = EXT4_SB(sb)->s_groups_count;
> + if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) {
> + elr->lr_next_group = ext4_mb_prefetch(sb, group,
> + EXT4_SB(sb)->s_mb_prefetch, &prefetch_ios);
> + if (prefetch_ios)
> + ext4_mb_prefetch_fini(sb, elr->lr_next_group,
> + prefetch_ios);
> + trace_ext4_prefetch_bitmaps(sb, group, elr->lr_next_group,
> + prefetch_ios);
> + if (group >= elr->lr_next_group) {
> + ret = 1;
> + if (elr->lr_first_not_zeroed != ngroups &&
> + !sb_rdonly(sb) && test_opt(sb, INIT_INODE_TABLE)) {
> + elr->lr_next_group = elr->lr_first_not_zeroed;
> + elr->lr_mode = EXT4_LI_MODE_ITABLE;
> + ret = 0;
> + }
> + }
> + return ret;
> + }
>
> - for (group = elr->lr_next_group; group < ngroups; group++) {
> + for (; group < ngroups; group++) {
> gdp = ext4_get_group_desc(sb, group, NULL);
> if (!gdp) {
> ret = 1;
> @@ -3227,9 +3250,10 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
> timeout = jiffies;
> ret = ext4_init_inode_table(sb, group,
> elr->lr_timeout ? 0 : 1);
> + trace_ext4_lazy_itable_init(sb, group);
> if (elr->lr_timeout == 0) {
> timeout = (jiffies - timeout) *
> - elr->lr_sbi->s_li_wait_mult;
> + EXT4_SB(elr->lr_super)->s_li_wait_mult;
> elr->lr_timeout = timeout;
> }
> elr->lr_next_sched = jiffies + elr->lr_timeout;
> @@ -3244,15 +3268,11 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
> */
> static void ext4_remove_li_request(struct ext4_li_request *elr)
> {
> - struct ext4_sb_info *sbi;
> -
> if (!elr)
> return;
>
> - sbi = elr->lr_sbi;
> -
> list_del(&elr->lr_request);
> - sbi->s_li_request = NULL;
> + EXT4_SB(elr->lr_super)->s_li_request = NULL;
> kfree(elr);
> }
>
> @@ -3461,7 +3481,6 @@ static int ext4_li_info_new(void)
> static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
> ext4_group_t start)
> {
> - struct ext4_sb_info *sbi = EXT4_SB(sb);
> struct ext4_li_request *elr;
>
> elr = kzalloc(sizeof(*elr), GFP_KERNEL);
> @@ -3469,8 +3488,13 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
> return NULL;
>
> elr->lr_super = sb;
> - elr->lr_sbi = sbi;
> - elr->lr_next_group = start;
> + elr->lr_first_not_zeroed = start;
> + if (test_opt(sb, PREFETCH_BLOCK_BITMAPS))
> + elr->lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP;
> + else {
> + elr->lr_mode = EXT4_LI_MODE_ITABLE;
> + elr->lr_next_group = start;
> + }
>
> /*
> * Randomize first schedule time of the request to
> @@ -3488,6 +3512,7 @@ int ext4_register_li_request(struct super_block *sb,
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> struct ext4_li_request *elr = NULL;
> ext4_group_t ngroups = sbi->s_groups_count;
> + enum ext4_li_mode lr_mode = EXT4_LI_MODE_ITABLE;
> int ret = 0;
>
> mutex_lock(&ext4_li_mtx);
> @@ -3500,8 +3525,10 @@ int ext4_register_li_request(struct super_block *sb,
> goto out;
> }
>
> - if (first_not_zeroed == ngroups || sb_rdonly(sb) ||
> - !test_opt(sb, INIT_INODE_TABLE))
> + if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) {
> + lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP;
> + } else if (first_not_zeroed == ngroups || sb_rdonly(sb) ||
> + !test_opt(sb, INIT_INODE_TABLE))
> goto out;
>
> elr = ext4_li_request_new(sb, first_not_zeroed);
> diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
> index cbcd2e1a608d..8008d2e116b9 100644
> --- a/include/trace/events/ext4.h
> +++ b/include/trace/events/ext4.h
> @@ -2742,6 +2742,50 @@ TRACE_EVENT(ext4_error,
> __entry->function, __entry->line)
> );
>
> +TRACE_EVENT(ext4_prefetch_bitmaps,
> + TP_PROTO(struct super_block *sb, ext4_group_t group,
> + ext4_group_t next, unsigned int prefetch_ios),
> +
> + TP_ARGS(sb, group, next, prefetch_ios),
> +
> + TP_STRUCT__entry(
> + __field( dev_t, dev )
> + __field( __u32, group )
> + __field( __u32, next )
> + __field( __u32, ios )
> + ),
> +
> + TP_fast_assign(
> + __entry->dev = sb->s_dev;
> + __entry->group = group;
> + __entry->next = next;
> + __entry->ios = prefetch_ios;
> + ),
> +
> + TP_printk("dev %d,%d group %u next %u ios %u",
> + MAJOR(__entry->dev), MINOR(__entry->dev),
> + __entry->group, __entry->next, __entry->ios)
> +);
> +
> +TRACE_EVENT(ext4_lazy_itable_init,
> + TP_PROTO(struct super_block *sb, ext4_group_t group),
> +
> + TP_ARGS(sb, group),
> +
> + TP_STRUCT__entry(
> + __field( dev_t, dev )
> + __field( __u32, group )
> + ),
> +
> + TP_fast_assign(
> + __entry->dev = sb->s_dev;
> + __entry->group = group;
> + ),
> +
> + TP_printk("dev %d,%d group %u",
> + MAJOR(__entry->dev), MINOR(__entry->dev), __entry->group)
> +);
> +
> #endif /* _TRACE_EXT4_H */
>
> /* This part must be outside protection */
> --
> 2.24.1
>
Cheers, Andreas
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