[PATCH v7 23/24] erofs: introduce cached decompression

From: Gao Xiang
Date: Tue Aug 13 2019 - 05:15:00 EST

This patch adds strategies which can be selected
by users in order to cache both incomplete ends of
compressed physical clusters as a complement of
in-place I/O in order to boost random read, but
it costs more memory than the in-place I/O only.

Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
fs/erofs/internal.h | 16 +++++
fs/erofs/super.c | 126 ++++++++++++++++++++++++++++++++-
fs/erofs/utils.c | 40 ++++++++---
fs/erofs/zdata.c | 165 ++++++++++++++++++++++++++++++++++++++++++--
fs/erofs/zdata.h | 7 +-
5 files changed, 336 insertions(+), 18 deletions(-)

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 5e2500f8d629..23eb4f50926e 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -72,6 +72,12 @@ struct erofs_sb_info {
unsigned int max_sync_decompress_pages;

unsigned int shrinker_run_no;
+
+ /* current strategy of how to use managed cache */
+ unsigned char cache_strategy;
+
+ /* pseudo inode to manage cached pages */
+ struct inode *managed_cache;
#endif /* CONFIG_EROFS_FS_ZIP */
u32 blocks;
u32 meta_blkaddr;
@@ -157,6 +163,12 @@ static inline void *erofs_kmalloc(struct erofs_sb_info *sbi,
#define test_opt(sbi, option) ((sbi)->mount_opt & EROFS_MOUNT_##option)

#ifdef CONFIG_EROFS_FS_ZIP
+enum {
+ EROFS_ZIP_CACHE_DISABLED,
+ EROFS_ZIP_CACHE_READAHEAD,
+ EROFS_ZIP_CACHE_READAROUND
+};
+
#define EROFS_LOCKED_MAGIC (INT_MIN | 0xE0F510CCL)

/* basic unit of the workstation of a super_block */
@@ -524,6 +536,10 @@ int __init erofs_init_shrinker(void);
void erofs_exit_shrinker(void);
int __init z_erofs_init_zip_subsystem(void);
void z_erofs_exit_zip_subsystem(void);
+int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
+ struct erofs_workgroup *egrp);
+int erofs_try_to_free_cached_page(struct address_space *mapping,
+ struct page *page);
#else
static inline void erofs_shrinker_register(struct super_block *sb) {}
static inline void erofs_shrinker_unregister(struct super_block *sb) {}
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index bdac8abf3aa7..95187619b3e3 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -197,10 +197,45 @@ static unsigned int erofs_get_fault_rate(struct erofs_sb_info *sbi)
}
#endif

+#ifdef CONFIG_EROFS_FS_ZIP
+static int erofs_build_cache_strategy(struct erofs_sb_info *sbi,
+ substring_t *args)
+{
+ const char *cs = match_strdup(args);
+ int err = 0;
+
+ if (!cs) {
+ errln("Not enough memory to store cache strategy");
+ return -ENOMEM;
+ }
+
+ if (!strcmp(cs, "disabled")) {
+ sbi->cache_strategy = EROFS_ZIP_CACHE_DISABLED;
+ } else if (!strcmp(cs, "readahead")) {
+ sbi->cache_strategy = EROFS_ZIP_CACHE_READAHEAD;
+ } else if (!strcmp(cs, "readaround")) {
+ sbi->cache_strategy = EROFS_ZIP_CACHE_READAROUND;
+ } else {
+ errln("Unrecognized cache strategy \"%s\"", cs);
+ err = -EINVAL;
+ }
+ kfree(cs);
+ return err;
+}
+#else
+static int erofs_build_cache_strategy(struct erofs_sb_info *sbi,
+ substring_t *args)
+{
+ infoln("EROFS compression is disabled, so cache strategy is ignored");
+ return 0;
+}
+#endif
+
/* set up default EROFS parameters */
static void default_options(struct erofs_sb_info *sbi)
{
#ifdef CONFIG_EROFS_FS_ZIP
+ sbi->cache_strategy = EROFS_ZIP_CACHE_READAROUND;
sbi->max_sync_decompress_pages = 3;
#endif
#ifdef CONFIG_EROFS_FS_XATTR
@@ -217,6 +252,7 @@ enum {
Opt_acl,
Opt_noacl,
Opt_fault_injection,
+ Opt_cache_strategy,
Opt_err
};

@@ -226,6 +262,7 @@ static match_table_t erofs_tokens = {
{Opt_acl, "acl"},
{Opt_noacl, "noacl"},
{Opt_fault_injection, "fault_injection=%u"},
+ {Opt_cache_strategy, "cache_strategy=%s"},
{Opt_err, NULL}
};

@@ -283,6 +320,11 @@ static int parse_options(struct super_block *sb, char *options)
if (err)
return err;
break;
+ case Opt_cache_strategy:
+ err = erofs_build_cache_strategy(EROFS_SB(sb), args);
+ if (err)
+ return err;
+ break;
default:
errln("Unrecognized mount option \"%s\" or missing value", p);
return -EINVAL;
@@ -291,6 +333,65 @@ static int parse_options(struct super_block *sb, char *options)
return 0;
}

+#ifdef CONFIG_EROFS_FS_ZIP
+static const struct address_space_operations managed_cache_aops;
+
+static int managed_cache_releasepage(struct page *page, gfp_t gfp_mask)
+{
+ int ret = 1; /* 0 - busy */
+ struct address_space *const mapping = page->mapping;
+
+ DBG_BUGON(!PageLocked(page));
+ DBG_BUGON(mapping->a_ops != &managed_cache_aops);
+
+ if (PagePrivate(page))
+ ret = erofs_try_to_free_cached_page(mapping, page);
+
+ return ret;
+}
+
+static void managed_cache_invalidatepage(struct page *page,
+ unsigned int offset,
+ unsigned int length)
+{
+ const unsigned int stop = length + offset;
+
+ DBG_BUGON(!PageLocked(page));
+
+ /* Check for potential overflow in debug mode */
+ DBG_BUGON(stop > PAGE_SIZE || stop < length);
+
+ if (offset == 0 && stop == PAGE_SIZE)
+ while (!managed_cache_releasepage(page, GFP_NOFS))
+ cond_resched();
+}
+
+static const struct address_space_operations managed_cache_aops = {
+ .releasepage = managed_cache_releasepage,
+ .invalidatepage = managed_cache_invalidatepage,
+};
+
+static int erofs_init_managed_cache(struct super_block *sb)
+{
+ struct erofs_sb_info *const sbi = EROFS_SB(sb);
+ struct inode *const inode = new_inode(sb);
+
+ if (unlikely(!inode))
+ return -ENOMEM;
+
+ set_nlink(inode, 1);
+ inode->i_size = OFFSET_MAX;
+
+ inode->i_mapping->a_ops = &managed_cache_aops;
+ mapping_set_gfp_mask(inode->i_mapping,
+ GFP_NOFS | __GFP_HIGHMEM | __GFP_MOVABLE);
+ sbi->managed_cache = inode;
+ return 0;
+}
+#else
+static int erofs_init_managed_cache(struct super_block *sb) { return 0; }
+#endif
+
static int erofs_fill_super(struct super_block *sb, void *data, int silent)
{
struct inode *inode;
@@ -325,7 +426,6 @@ static int erofs_fill_super(struct super_block *sb, void *data, int silent)
#ifdef CONFIG_EROFS_FS_XATTR
sb->s_xattr = erofs_xattr_handlers;
#endif
-
/* set erofs default mount options */
default_options(sbi);

@@ -362,6 +462,10 @@ static int erofs_fill_super(struct super_block *sb, void *data, int silent)
return -ENOMEM;

erofs_shrinker_register(sb);
+ /* sb->s_umount is already locked, SB_ACTIVE and SB_BORN are not set */
+ err = erofs_init_managed_cache(sb);
+ if (unlikely(err))
+ return err;

if (!silent)
infoln("mounted on %s with opts: %s.", sb->s_id, (char *)data);
@@ -397,7 +501,15 @@ static void erofs_kill_sb(struct super_block *sb)
/* called when ->s_root is non-NULL */
static void erofs_put_super(struct super_block *sb)
{
+ struct erofs_sb_info *const sbi = EROFS_SB(sb);
+
+ DBG_BUGON(!sbi);
+
erofs_shrinker_unregister(sb);
+#ifdef CONFIG_EROFS_FS_ZIP
+ iput(sbi->managed_cache);
+ sbi->managed_cache = NULL;
+#endif
}

static struct file_system_type erofs_fs_type = {
@@ -495,6 +607,18 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
if (test_opt(sbi, FAULT_INJECTION))
seq_printf(seq, ",fault_injection=%u",
erofs_get_fault_rate(sbi));
+#ifdef CONFIG_EROFS_FS_ZIP
+ if (sbi->cache_strategy == EROFS_ZIP_CACHE_DISABLED) {
+ seq_puts(seq, ",cache_strategy=disabled");
+ } else if (sbi->cache_strategy == EROFS_ZIP_CACHE_READAHEAD) {
+ seq_puts(seq, ",cache_strategy=readahead");
+ } else if (sbi->cache_strategy == EROFS_ZIP_CACHE_READAROUND) {
+ seq_puts(seq, ",cache_strategy=readaround");
+ } else {
+ seq_puts(seq, ",cache_strategy=(unknown)");
+ DBG_BUGON(1);
+ }
+#endif
return 0;
}

diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index ae6362abed67..c48e417d3926 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -144,24 +144,48 @@ int erofs_workgroup_put(struct erofs_workgroup *grp)
return count;
}

-/* for nocache case, no customized reclaim path at all */
+static void erofs_workgroup_unfreeze_final(struct erofs_workgroup *grp)
+{
+ erofs_workgroup_unfreeze(grp, 0);
+ __erofs_workgroup_free(grp);
+}
+
static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
struct erofs_workgroup *grp,
bool cleanup)
{
- int cnt = atomic_read(&grp->refcount);
-
- DBG_BUGON(cnt <= 0);
- DBG_BUGON(cleanup && cnt != 1);
+ /*
+ * If managed cache is on, refcount of workgroups
+ * themselves could be < 0 (freezed). In other words,
+ * there is no guarantee that all refcounts > 0.
+ */
+ if (!erofs_workgroup_try_to_freeze(grp, 1))
+ return false;

- if (cnt > 1)
+ /*
+ * Note that all cached pages should be unattached
+ * before deleted from the radix tree. Otherwise some
+ * cached pages could be still attached to the orphan
+ * old workgroup when the new one is available in the tree.
+ */
+ if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
+ erofs_workgroup_unfreeze(grp, 1);
return false;
+ }

+ /*
+ * It's impossible to fail after the workgroup is freezed,
+ * however in order to avoid some race conditions, add a
+ * DBG_BUGON to observe this in advance.
+ */
DBG_BUGON(xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
grp->index)) != grp);

- /* (rarely) could be grabbed again when freeing */
- erofs_workgroup_put(grp);
+ /*
+ * If managed cache is on, last refcount should indicate
+ * the related workstation.
+ */
+ erofs_workgroup_unfreeze_final(grp);
return true;
}

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index ffa64b1d8908..24be7d98bce3 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -167,7 +167,110 @@ static void preload_compressed_pages(struct z_erofs_collector *clt,
enum z_erofs_cache_alloctype type,
struct list_head *pagepool)
{
- /* nowhere to load compressed pages from */
+ const struct z_erofs_pcluster *pcl = clt->pcl;
+ const unsigned int clusterpages = BIT(pcl->clusterbits);
+ struct page **pages = clt->compressedpages;
+ pgoff_t index = pcl->obj.index + (pages - pcl->compressed_pages);
+ bool standalone = true;
+
+ if (clt->mode < COLLECT_PRIMARY_FOLLOWED)
+ return;
+
+ for (; pages < pcl->compressed_pages + clusterpages; ++pages) {
+ struct page *page;
+ compressed_page_t t;
+
+ /* the compressed page was loaded before */
+ if (READ_ONCE(*pages))
+ continue;
+
+ page = find_get_page(mc, index);
+
+ if (page) {
+ t = tag_compressed_page_justfound(page);
+ } else if (type == DELAYEDALLOC) {
+ t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);
+ } else { /* DONTALLOC */
+ if (standalone)
+ clt->compressedpages = pages;
+ standalone = false;
+ continue;
+ }
+
+ if (!cmpxchg_relaxed(pages, NULL, tagptr_cast_ptr(t)))
+ continue;
+
+ if (page)
+ put_page(page);
+ }
+
+ if (standalone) /* downgrade to PRIMARY_FOLLOWED_NOINPLACE */
+ clt->mode = COLLECT_PRIMARY_FOLLOWED_NOINPLACE;
+}
+
+/* called by erofs_shrinker to get rid of all compressed_pages */
+int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
+ struct erofs_workgroup *grp)
+{
+ struct z_erofs_pcluster *const pcl =
+ container_of(grp, struct z_erofs_pcluster, obj);
+ struct address_space *const mapping = MNGD_MAPPING(sbi);
+ const unsigned int clusterpages = BIT(pcl->clusterbits);
+ int i;
+
+ /*
+ * refcount of workgroup is now freezed as 1,
+ * therefore no need to worry about available decompression users.
+ */
+ for (i = 0; i < clusterpages; ++i) {
+ struct page *page = pcl->compressed_pages[i];
+
+ if (!page)
+ continue;
+
+ /* block other users from reclaiming or migrating the page */
+ if (!trylock_page(page))
+ return -EBUSY;
+
+ if (unlikely(page->mapping != mapping))
+ continue;
+
+ /* barrier is implied in the following 'unlock_page' */
+ WRITE_ONCE(pcl->compressed_pages[i], NULL);
+ set_page_private(page, 0);
+ ClearPagePrivate(page);
+
+ unlock_page(page);
+ put_page(page);
+ }
+ return 0;
+}
+
+int erofs_try_to_free_cached_page(struct address_space *mapping,
+ struct page *page)
+{
+ struct z_erofs_pcluster *const pcl = (void *)page_private(page);
+ const unsigned int clusterpages = BIT(pcl->clusterbits);
+ int ret = 0; /* 0 - busy */
+
+ if (erofs_workgroup_try_to_freeze(&pcl->obj, 1)) {
+ unsigned int i;
+
+ for (i = 0; i < clusterpages; ++i) {
+ if (pcl->compressed_pages[i] == page) {
+ WRITE_ONCE(pcl->compressed_pages[i], NULL);
+ ret = 1;
+ break;
+ }
+ }
+ erofs_workgroup_unfreeze(&pcl->obj, 1);
+
+ if (ret) {
+ ClearPagePrivate(page);
+ put_page(page);
+ }
+ }
+ return ret;
}

/* page_type must be Z_EROFS_PAGE_TYPE_EXCLUSIVE */
@@ -434,6 +537,20 @@ static inline struct page *__stagingpage_alloc(struct list_head *pagepool,
return page;
}

+static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
+ unsigned int cachestrategy,
+ erofs_off_t la)
+{
+ if (cachestrategy <= EROFS_ZIP_CACHE_DISABLED)
+ return false;
+
+ if (fe->backmost)
+ return true;
+
+ return cachestrategy >= EROFS_ZIP_CACHE_READAROUND &&
+ la < fe->headoffset;
+}
+
static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
struct page *page,
struct list_head *pagepool)
@@ -488,7 +605,13 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
goto err_out;

/* preload all compressed pages (maybe downgrade role if necessary) */
- preload_compressed_pages(clt, MNGD_MAPPING(sbi), DONTALLOC, pagepool);
+ if (should_alloc_managed_pages(fe, sbi->cache_strategy, map->m_la))
+ cache_strategy = DELAYEDALLOC;
+ else
+ cache_strategy = DONTALLOC;
+
+ preload_compressed_pages(clt, MNGD_MAPPING(sbi),
+ cache_strategy, pagepool);

tight &= (clt->mode >= COLLECT_PRIMARY_HOOKED);
hitted:
@@ -987,6 +1110,7 @@ static struct z_erofs_unzip_io *jobqueue_init(struct super_block *sb,

/* define decompression jobqueue types */
enum {
+ JQ_BYPASS,
JQ_SUBMIT,
NR_JOBQUEUES,
};
@@ -997,6 +1121,13 @@ static void *jobqueueset_init(struct super_block *sb,
struct z_erofs_unzip_io *fgq,
bool forcefg)
{
+ /*
+ * if managed cache is enabled, bypass jobqueue is needed,
+ * no need to read from device for all pclusters in this queue.
+ */
+ q[JQ_BYPASS] = jobqueue_init(sb, fgq + JQ_BYPASS, true);
+ qtail[JQ_BYPASS] = &q[JQ_BYPASS]->head;
+
q[JQ_SUBMIT] = jobqueue_init(sb, fgq + JQ_SUBMIT, forcefg);
qtail[JQ_SUBMIT] = &q[JQ_SUBMIT]->head;

@@ -1007,17 +1138,34 @@ static void move_to_bypass_jobqueue(struct z_erofs_pcluster *pcl,
z_erofs_next_pcluster_t qtail[],
z_erofs_next_pcluster_t owned_head)
{
- /* impossible to bypass submission for managed cache disabled */
- DBG_BUGON(1);
+ z_erofs_next_pcluster_t *const submit_qtail = qtail[JQ_SUBMIT];
+ z_erofs_next_pcluster_t *const bypass_qtail = qtail[JQ_BYPASS];
+
+ DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
+ if (owned_head == Z_EROFS_PCLUSTER_TAIL)
+ owned_head = Z_EROFS_PCLUSTER_TAIL_CLOSED;
+
+ WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_TAIL_CLOSED);
+
+ WRITE_ONCE(*submit_qtail, owned_head);
+ WRITE_ONCE(*bypass_qtail, &pcl->next);
+
+ qtail[JQ_BYPASS] = &pcl->next;
}

static bool postsubmit_is_all_bypassed(struct z_erofs_unzip_io *q[],
unsigned int nr_bios,
bool force_fg)
{
- /* bios should be >0 if managed cache is disabled */
- DBG_BUGON(!nr_bios);
- return false;
+ /*
+ * although background is preferred, no one is pending for submission.
+ * don't issue workqueue for decompression but drop it directly instead.
+ */
+ if (force_fg || nr_bios)
+ return false;
+
+ kvfree(container_of(q[JQ_SUBMIT], struct z_erofs_unzip_io_sb, io));
+ return true;
}

static bool z_erofs_vle_submit_all(struct super_block *sb,
@@ -1130,6 +1278,9 @@ static void z_erofs_submit_and_unzip(struct super_block *sb,
pagepool, io, force_fg))
return;

+ /* decompress no I/O pclusters immediately */
+ z_erofs_vle_unzip_all(sb, &io[JQ_BYPASS], pagepool);
+
if (!force_fg)
return;

diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
index 3a82ae933015..506ca46727db 100644
--- a/fs/erofs/zdata.h
+++ b/fs/erofs/zdata.h
@@ -101,9 +101,12 @@ struct z_erofs_unzip_io_sb {
struct super_block *sb;
};

-#define MNGD_MAPPING(sbi) (NULL)
+#define MNGD_MAPPING(sbi) ((sbi)->managed_cache->i_mapping)
static inline bool erofs_page_is_managed(const struct erofs_sb_info *sbi,
- struct page *page) { return false; }
+ struct page *page)
+{
+ return page->mapping == MNGD_MAPPING(sbi);
+}

#define Z_EROFS_ONLINEPAGE_COUNT_BITS 2
#define Z_EROFS_ONLINEPAGE_COUNT_MASK ((1 << Z_EROFS_ONLINEPAGE_COUNT_BITS) - 1)
--
2.17.1