[lustre-devel] [PATCH 17/39] lustre: llite: try to improve mmap performance
James Simmons
jsimmons at infradead.org
Thu Jan 21 09:16:40 PST 2021
From: Wang Shilong <wshilong at ddn.com>
We have observed slow mmap read performances for some
applications. The problem is if access pattern is neither
sequential nor stride, but could be still adjacent in a
small range and then seek a random position.
So the pattern could be something like this:
[1M data] [hole] [0.5M data] [hole] [0.7M data] [1M data]
Every time an application reads mmap data, it may not only
read a single 4KB page, but aslo a cluster of nearby pages in
a range(e.g. 1MB) of the first page after a cache miss.
The readahead engine is modified to track the range size of
a cluster of mmap reads, so that after a seek and/or cache miss,
the range size is used to efficiently prefetch multiple pages
in a single RPC rather than many small RPCs.
Benchmark:
fio --name=randread --directory=/ai400/fio --rw=randread
--ioengine=mmap --bs=128K --numjobs=32 --filesize=200G
--filename=randread --time_based --status-interval=10s
--runtime=30s --allow_file_create=1 --group_reporting
--disable_lat=1 --disable_clat=1 --disable_slat=1
--disk_util=0 --aux-path=/tmp --randrepeat=0
--unique_filename=0 --fallocate=0
| master | patched | speedup |
---------------+-----------+------------+-----------+
page_fault_avg | 512usec | 52usec | 9.75x
page_fault_max | 37698usec| 6543usec| 5.76x
WC-bug-id: https://jira.whamcloud.com/browse/LU-13669
Lustre-commit: 0c5ad4b6df5bf3 ("LU-13669 llite: try to improve mmap performance")
Signed-off-by: Wang Shilong <wshilong at ddn.com>
Reviewed-on: https://review.whamcloud.com/38916
Reviewed-by: Andreas Dilger <adilger at whamcloud.com>
Reviewed-by: Yingjin Qian <qian at ddn.com>
Reviewed-by: Oleg Drokin <green at whamcloud.com>
Signed-off-by: James Simmons <jsimmons at infradead.org>
---
fs/lustre/llite/llite_internal.h | 18 +++++
fs/lustre/llite/llite_lib.c | 1 +
fs/lustre/llite/lproc_llite.c | 47 +++++++++++++
fs/lustre/llite/rw.c | 142 +++++++++++++++++++++++++++++++++++----
4 files changed, 196 insertions(+), 12 deletions(-)
diff --git a/fs/lustre/llite/llite_internal.h b/fs/lustre/llite/llite_internal.h
index bad974f..797dfea 100644
--- a/fs/lustre/llite/llite_internal.h
+++ b/fs/lustre/llite/llite_internal.h
@@ -482,6 +482,12 @@ static inline struct pcc_inode *ll_i2pcci(struct inode *inode)
/* default read-ahead full files smaller than limit on the second read */
#define SBI_DEFAULT_READ_AHEAD_WHOLE_MAX MiB_TO_PAGES(2UL)
+/* default range pages */
+#define SBI_DEFAULT_RA_RANGE_PAGES MiB_TO_PAGES(1ULL)
+
+/* Min range pages */
+#define RA_MIN_MMAP_RANGE_PAGES 16UL
+
enum ra_stat {
RA_STAT_HIT = 0,
RA_STAT_MISS,
@@ -498,6 +504,7 @@ enum ra_stat {
RA_STAT_FAILED_REACH_END,
RA_STAT_ASYNC,
RA_STAT_FAILED_FAST_READ,
+ RA_STAT_MMAP_RANGE_READ,
_NR_RA_STAT,
};
@@ -505,6 +512,7 @@ struct ll_ra_info {
atomic_t ra_cur_pages;
unsigned long ra_max_pages;
unsigned long ra_max_pages_per_file;
+ unsigned long ra_range_pages;
unsigned long ra_max_read_ahead_whole_pages;
struct workqueue_struct *ll_readahead_wq;
/*
@@ -790,6 +798,16 @@ struct ll_readahead_state {
*/
pgoff_t ras_window_start_idx;
pgoff_t ras_window_pages;
+
+ /* Page index where min range read starts */
+ pgoff_t ras_range_min_start_idx;
+ /* Page index where mmap range read ends */
+ pgoff_t ras_range_max_end_idx;
+ /* number of mmap pages where last time detected */
+ pgoff_t ras_last_range_pages;
+ /* number of mmap range requests */
+ pgoff_t ras_range_requests;
+
/*
* Optimal RPC size in pages.
* It decides how many pages will be sent for each read-ahead.
diff --git a/fs/lustre/llite/llite_lib.c b/fs/lustre/llite/llite_lib.c
index 34bd661..c560492 100644
--- a/fs/lustre/llite/llite_lib.c
+++ b/fs/lustre/llite/llite_lib.c
@@ -130,6 +130,7 @@ static struct ll_sb_info *ll_init_sbi(void)
SBI_DEFAULT_READ_AHEAD_PER_FILE_MAX);
sbi->ll_ra_info.ra_async_pages_per_file_threshold =
sbi->ll_ra_info.ra_max_pages_per_file;
+ sbi->ll_ra_info.ra_range_pages = SBI_DEFAULT_RA_RANGE_PAGES;
sbi->ll_ra_info.ra_max_read_ahead_whole_pages = -1;
atomic_set(&sbi->ll_ra_info.ra_async_inflight, 0);
diff --git a/fs/lustre/llite/lproc_llite.c b/fs/lustre/llite/lproc_llite.c
index 9b1c392..5d1e2f4 100644
--- a/fs/lustre/llite/lproc_llite.c
+++ b/fs/lustre/llite/lproc_llite.c
@@ -1173,6 +1173,51 @@ static ssize_t read_ahead_async_file_threshold_mb_show(struct kobject *kobj,
}
LUSTRE_RW_ATTR(read_ahead_async_file_threshold_mb);
+static ssize_t read_ahead_range_kb_show(struct kobject *kobj,
+ struct attribute *attr, char *buf)
+{
+ struct ll_sb_info *sbi = container_of(kobj, struct ll_sb_info,
+ ll_kset.kobj);
+
+ return scnprintf(buf, PAGE_SIZE, "%lu\n",
+ sbi->ll_ra_info.ra_range_pages << (PAGE_SHIFT - 10));
+}
+
+static ssize_t
+read_ahead_range_kb_store(struct kobject *kobj,
+ struct attribute *attr,
+ const char *buffer, size_t count)
+{
+ struct ll_sb_info *sbi = container_of(kobj, struct ll_sb_info,
+ ll_kset.kobj);
+ unsigned long pages_number;
+ unsigned long max_ra_per_file;
+ u64 val;
+ int rc;
+
+ rc = sysfs_memparse(buffer, count, &val, "KiB");
+ if (rc < 0)
+ return rc;
+
+ pages_number = val >> PAGE_SHIFT;
+ /* Disable mmap range read */
+ if (pages_number == 0)
+ goto out;
+
+ max_ra_per_file = sbi->ll_ra_info.ra_max_pages_per_file;
+ if (pages_number > max_ra_per_file ||
+ pages_number < RA_MIN_MMAP_RANGE_PAGES)
+ return -ERANGE;
+
+out:
+ spin_lock(&sbi->ll_lock);
+ sbi->ll_ra_info.ra_range_pages = pages_number;
+ spin_unlock(&sbi->ll_lock);
+
+ return count;
+}
+LUSTRE_RW_ATTR(read_ahead_range_kb);
+
static ssize_t fast_read_show(struct kobject *kobj,
struct attribute *attr,
char *buf)
@@ -1506,6 +1551,7 @@ struct ldebugfs_vars lprocfs_llite_obd_vars[] = {
&lustre_attr_max_read_ahead_mb.attr,
&lustre_attr_max_read_ahead_per_file_mb.attr,
&lustre_attr_max_read_ahead_whole_mb.attr,
+ &lustre_attr_read_ahead_range_kb.attr,
&lustre_attr_checksums.attr,
&lustre_attr_checksum_pages.attr,
&lustre_attr_stats_track_pid.attr,
@@ -1622,6 +1668,7 @@ void ll_stats_ops_tally(struct ll_sb_info *sbi, int op, long count)
[RA_STAT_FAILED_REACH_END] = "failed to reach end",
[RA_STAT_ASYNC] = "async readahead",
[RA_STAT_FAILED_FAST_READ] = "failed to fast read",
+ [RA_STAT_MMAP_RANGE_READ] = "mmap range read",
};
int ll_debugfs_register_super(struct super_block *sb, const char *name)
diff --git a/fs/lustre/llite/rw.c b/fs/lustre/llite/rw.c
index da4a26d..096e015 100644
--- a/fs/lustre/llite/rw.c
+++ b/fs/lustre/llite/rw.c
@@ -388,7 +388,7 @@ static bool ras_inside_ra_window(pgoff_t idx, struct ra_io_arg *ria)
static unsigned long
ll_read_ahead_pages(const struct lu_env *env, struct cl_io *io,
struct cl_page_list *queue, struct ll_readahead_state *ras,
- struct ra_io_arg *ria, pgoff_t *ra_end)
+ struct ra_io_arg *ria, pgoff_t *ra_end, pgoff_t skip_index)
{
struct cl_read_ahead ra = { 0 };
pgoff_t page_idx;
@@ -402,6 +402,8 @@ static bool ras_inside_ra_window(pgoff_t idx, struct ra_io_arg *ria)
for (page_idx = ria->ria_start_idx;
page_idx <= ria->ria_end_idx && ria->ria_reserved > 0;
page_idx++) {
+ if (skip_index && page_idx == skip_index)
+ continue;
if (ras_inside_ra_window(page_idx, ria)) {
if (!ra.cra_end_idx || ra.cra_end_idx < page_idx) {
pgoff_t end_idx;
@@ -447,10 +449,12 @@ static bool ras_inside_ra_window(pgoff_t idx, struct ra_io_arg *ria)
if (ras->ras_rpc_pages != ra.cra_rpc_pages &&
ra.cra_rpc_pages > 0)
ras->ras_rpc_pages = ra.cra_rpc_pages;
- /* trim it to align with optimal RPC size */
- end_idx = ras_align(ras, ria->ria_end_idx + 1);
- if (end_idx > 0 && !ria->ria_eof)
- ria->ria_end_idx = end_idx - 1;
+ if (!skip_index) {
+ /* trim it to align with optimal RPC size */
+ end_idx = ras_align(ras, ria->ria_end_idx + 1);
+ if (end_idx > 0 && !ria->ria_eof)
+ ria->ria_end_idx = end_idx - 1;
+ }
if (ria->ria_end_idx < ria->ria_end_idx_min)
ria->ria_end_idx = ria->ria_end_idx_min;
}
@@ -650,7 +654,7 @@ static void ll_readahead_handle_work(struct work_struct *wq)
cl_2queue_init(queue);
rc = ll_read_ahead_pages(env, io, &queue->c2_qin, ras, ria,
- &ra_end_idx);
+ &ra_end_idx, 0);
if (ria->ria_reserved != 0)
ll_ra_count_put(ll_i2sbi(inode), ria->ria_reserved);
if (queue->c2_qin.pl_nr > 0) {
@@ -688,7 +692,7 @@ static void ll_readahead_handle_work(struct work_struct *wq)
static int ll_readahead(const struct lu_env *env, struct cl_io *io,
struct cl_page_list *queue,
struct ll_readahead_state *ras, bool hit,
- struct file *file)
+ struct file *file, pgoff_t skip_index)
{
struct vvp_io *vio = vvp_env_io(env);
struct ll_thread_info *lti = ll_env_info(env);
@@ -731,6 +735,9 @@ static int ll_readahead(const struct lu_env *env, struct cl_io *io,
if (ras->ras_window_pages > 0)
end_idx = ras->ras_window_start_idx + ras->ras_window_pages - 1;
+ if (skip_index)
+ end_idx = start_idx + ras->ras_window_pages - 1;
+
/* Enlarge the RA window to encompass the full read */
if (vio->vui_ra_valid &&
end_idx < vio->vui_ra_start_idx + vio->vui_ra_pages - 1)
@@ -783,6 +790,10 @@ static int ll_readahead(const struct lu_env *env, struct cl_io *io,
ria->ria_start_idx;
}
+ /* don't over reserved for mmap range read */
+ if (skip_index)
+ pages_min = 0;
+
ria->ria_reserved = ll_ra_count_get(ll_i2sbi(inode), ria, pages,
pages_min);
if (ria->ria_reserved < pages)
@@ -793,8 +804,8 @@ static int ll_readahead(const struct lu_env *env, struct cl_io *io,
atomic_read(&ll_i2sbi(inode)->ll_ra_info.ra_cur_pages),
ll_i2sbi(inode)->ll_ra_info.ra_max_pages);
- ret = ll_read_ahead_pages(env, io, queue, ras, ria, &ra_end_idx);
-
+ ret = ll_read_ahead_pages(env, io, queue, ras, ria, &ra_end_idx,
+ skip_index);
if (ria->ria_reserved)
ll_ra_count_put(ll_i2sbi(inode), ria->ria_reserved);
@@ -890,6 +901,10 @@ void ll_readahead_init(struct inode *inode, struct ll_readahead_state *ras)
ras_reset(ras, 0);
ras->ras_last_read_end_bytes = 0;
ras->ras_requests = 0;
+ ras->ras_range_min_start_idx = 0;
+ ras->ras_range_max_end_idx = 0;
+ ras->ras_range_requests = 0;
+ ras->ras_last_range_pages = 0;
}
/*
@@ -1033,6 +1048,73 @@ static inline bool is_loose_seq_read(struct ll_readahead_state *ras, loff_t pos)
8UL << PAGE_SHIFT, 8UL << PAGE_SHIFT);
}
+static inline bool is_loose_mmap_read(struct ll_sb_info *sbi,
+ struct ll_readahead_state *ras,
+ unsigned long pos)
+{
+ unsigned long range_pages = sbi->ll_ra_info.ra_range_pages;
+
+ return pos_in_window(pos, ras->ras_last_read_end_bytes,
+ range_pages << PAGE_SHIFT,
+ range_pages << PAGE_SHIFT);
+}
+
+/**
+ * We have observed slow mmap read performances for some
+ * applications. The problem is if access pattern is neither
+ * sequential nor stride, but could be still adjacent in a
+ * small range and then seek a random position.
+ *
+ * So the pattern could be something like this:
+ *
+ * [1M data] [hole] [0.5M data] [hole] [0.7M data] [1M data]
+ *
+ *
+ * Every time an application reads mmap data, it may not only
+ * read a single 4KB page, but aslo a cluster of nearby pages in
+ * a range(e.g. 1MB) of the first page after a cache miss.
+ *
+ * The readahead engine is modified to track the range size of
+ * a cluster of mmap reads, so that after a seek and/or cache miss,
+ * the range size is used to efficiently prefetch multiple pages
+ * in a single RPC rather than many small RPCs.
+ */
+static void ras_detect_cluster_range(struct ll_readahead_state *ras,
+ struct ll_sb_info *sbi,
+ unsigned long pos, unsigned long count)
+{
+ pgoff_t last_pages, pages;
+ pgoff_t end_idx = (pos + count - 1) >> PAGE_SHIFT;
+
+ last_pages = ras->ras_range_max_end_idx -
+ ras->ras_range_min_start_idx + 1;
+ /* First time come here */
+ if (!ras->ras_range_max_end_idx)
+ goto out;
+
+ /* Random or Stride read */
+ if (!is_loose_mmap_read(sbi, ras, pos))
+ goto out;
+
+ ras->ras_range_requests++;
+ if (ras->ras_range_max_end_idx < end_idx)
+ ras->ras_range_max_end_idx = end_idx;
+
+ if (ras->ras_range_min_start_idx > (pos >> PAGE_SHIFT))
+ ras->ras_range_min_start_idx = pos >> PAGE_SHIFT;
+
+ /* Out of range, consider it as random or stride */
+ pages = ras->ras_range_max_end_idx -
+ ras->ras_range_min_start_idx + 1;
+ if (pages <= sbi->ll_ra_info.ra_range_pages)
+ return;
+out:
+ ras->ras_last_range_pages = last_pages;
+ ras->ras_range_requests = 0;
+ ras->ras_range_min_start_idx = pos >> PAGE_SHIFT;
+ ras->ras_range_max_end_idx = end_idx;
+}
+
static void ras_detect_read_pattern(struct ll_readahead_state *ras,
struct ll_sb_info *sbi,
loff_t pos, size_t count, bool mmap)
@@ -1080,9 +1162,13 @@ static void ras_detect_read_pattern(struct ll_readahead_state *ras,
ras->ras_consecutive_bytes += count;
if (mmap) {
+ unsigned long ra_range_pages =
+ max_t(unsigned long, RA_MIN_MMAP_RANGE_PAGES,
+ sbi->ll_ra_info.ra_range_pages);
pgoff_t idx = ras->ras_consecutive_bytes >> PAGE_SHIFT;
- if ((idx >= 4 && (idx & 3UL) == 0) || stride_detect)
+ if ((idx >= ra_range_pages &&
+ idx % ra_range_pages == 0) || stride_detect)
ras->ras_need_increase_window = true;
} else if ((ras->ras_consecutive_requests > 1 || stride_detect)) {
ras->ras_need_increase_window = true;
@@ -1190,10 +1276,36 @@ static void ras_update(struct ll_sb_info *sbi, struct inode *inode,
if (ras->ras_no_miss_check)
goto out_unlock;
- if (flags & LL_RAS_MMAP)
+ if (flags & LL_RAS_MMAP) {
+ unsigned long ra_pages;
+
+ ras_detect_cluster_range(ras, sbi, index << PAGE_SHIFT,
+ PAGE_SIZE);
ras_detect_read_pattern(ras, sbi, (loff_t)index << PAGE_SHIFT,
PAGE_SIZE, true);
+ /* we did not detect anything but we could prefetch */
+ if (!ras->ras_need_increase_window &&
+ ras->ras_window_pages <= sbi->ll_ra_info.ra_range_pages &&
+ ras->ras_range_requests >= 2) {
+ if (!hit) {
+ ra_pages = max_t(unsigned long,
+ RA_MIN_MMAP_RANGE_PAGES,
+ ras->ras_last_range_pages);
+ if (index < ra_pages / 2)
+ index = 0;
+ else
+ index -= ra_pages / 2;
+ ras->ras_window_pages = ra_pages;
+ ll_ra_stats_inc_sbi(sbi,
+ RA_STAT_MMAP_RANGE_READ);
+ } else {
+ ras->ras_window_pages = 0;
+ }
+ goto skip;
+ }
+ }
+
if (!hit && ras->ras_window_pages &&
index < ras->ras_next_readahead_idx &&
pos_in_window(index, ras->ras_window_start_idx, 0,
@@ -1231,6 +1343,8 @@ static void ras_update(struct ll_sb_info *sbi, struct inode *inode,
goto out_unlock;
}
}
+
+skip:
ras_set_start(ras, index);
if (stride_io_mode(ras)) {
@@ -1500,8 +1614,12 @@ int ll_io_read_page(const struct lu_env *env, struct cl_io *io,
io_end_index = cl_index(io->ci_obj, io->u.ci_rw.crw_pos +
io->u.ci_rw.crw_count - 1);
if (ll_readahead_enabled(sbi) && ras) {
+ pgoff_t skip_index = 0;
+
+ if (ras->ras_next_readahead_idx < vvp_index(vpg))
+ skip_index = vvp_index(vpg);
rc2 = ll_readahead(env, io, &queue->c2_qin, ras,
- uptodate, file);
+ uptodate, file, skip_index);
CDEBUG(D_READA, DFID " %d pages read ahead at %lu\n",
PFID(ll_inode2fid(inode)), rc2, vvp_index(vpg));
} else if (vvp_index(vpg) == io_start_index &&
--
1.8.3.1
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