[PATCH v3 23/24] erofs: introduce cached decompression

Gao Xiang
2019-07-22T02:51:41Z

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@huawei.com>
---
fs/erofs/Kconfig | 38 ++++++++++
fs/erofs/internal.h | 17 +++++
fs/erofs/super.c | 15 +++-
fs/erofs/utils.c | 104 ++++++++++++++++++++++++++-
fs/erofs/zdata.c | 171 ++++++++++++++++++++++++++++++++++++++++++++
fs/erofs/zdata.h | 9 +++
6 files changed, 352 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 5eb5cf1148a5..7fde54f76d5b 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -114,3 +114,41 @@ config EROFS_FS_CLUSTER_PAGE_LIMIT
less than 2. Otherwise, the image will be refused
to mount on this kernel.

+choice
+ prompt "EROFS Data Decompression mode"
+ depends on EROFS_FS_ZIP
+ default EROFS_FS_ZIP_CACHE_READAROUND
+ help
+ EROFS supports three options for decompression.
+ "In-place I/O Only" consumes the minimum memory
+ with lowest random read.
+
+ "Cached Decompression for readaround" consumes
+ the maximum memory with highest random read.
+
+ If unsure, select "Cached Decompression for readaround"
+
+config EROFS_FS_ZIP_CACHE_DISABLED
+ bool "In-place I/O Only"
+ help
+ Read compressed data into page cache and do in-place
+ I/O decompression directly.
+
+config EROFS_FS_ZIP_CACHE_READAHEAD
+ bool "Cached Decompression for readahead"
+ help
+ For each request, it caches the last compressed page
+ for further reading.
+ It still does in-place I/O for the rest compressed pages.
+
+config EROFS_FS_ZIP_CACHE_READAROUND
+ bool "Cached Decompression for readaround"
+ help
+ For each request, it caches the both end compressed pages
+ for further reading.
+ It still does in-place I/O for the rest compressed pages.
+
+ Recommended for performance priority.
+
+endchoice
+
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 1092a80a212e..91a4608499af 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -52,6 +52,11 @@ struct erofs_fault_info {
};
#endif

+#ifdef CONFIG_EROFS_FS_ZIP_CACHE_READAROUND
+#define EROFS_FS_HAS_MANAGED_CACHE (2)
+#elif defined(CONFIG_EROFS_FS_ZIP_CACHE_READAHEAD)
+#define EROFS_FS_HAS_MANAGED_CACHE (1)
+#endif
/* EROFS_SUPER_MAGIC_V1 to represent the whole file system */
#define EROFS_SUPER_MAGIC EROFS_SUPER_MAGIC_V1

@@ -74,6 +79,10 @@ struct erofs_sb_info {

unsigned int shrinker_run_no;
#endif
+
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ struct inode *managed_cache;
+#endif
u32 blocks;
u32 meta_blkaddr;
#ifdef CONFIG_EROFS_FS_XATTR
@@ -545,5 +554,13 @@ static inline int z_erofs_init_zip_subsystem(void) { return 0; }
static inline void z_erofs_exit_zip_subsystem(void) {}
#endif

+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+struct inode *erofs_init_managed_cache(struct super_block *sb);
+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);
+#endif
+
#endif

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index bd45a674dea9..aa4bbfde6f8e 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -327,7 +327,6 @@ 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);

@@ -364,6 +363,12 @@ static int erofs_fill_super(struct super_block *sb, void *data, int silent)
return -ENOMEM;

erofs_shrinker_register(sb);
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ /* sb->s_umount is locked here, SB_ACTIVE and SB_BORN are not set */
+ sbi->managed_cache = erofs_init_managed_cache(sb);
+ if (unlikely(!sbi->managed_cache))
+ return -ENOMEM;
+#endif

if (!silent)
infoln("mounted on %s with opts: %s.", sb->s_id, (char *)data);
@@ -399,6 +404,14 @@ 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);
+
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ iput(sbi->managed_cache);
+ sbi->managed_cache = NULL;
+#endif
erofs_shrinker_unregister(sb);
}

diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index 53ee6daa3f70..359d3357701d 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -145,6 +145,53 @@ int erofs_workgroup_put(struct erofs_workgroup *grp)
return count;
}

+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+/* for cache-managed case, customized reclaim paths exist */
+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)
+{
+ /*
+ * for managed cache enabled, the refcount of workgroups
+ * themselves could be < 0 (freezed). So there is no guarantee
+ * that all refcount > 0 if managed cache is enabled.
+ */
+ if (!erofs_workgroup_try_to_freeze(grp, 1))
+ return false;
+
+ /*
+ * note that all cached pages should be unlinked
+ * before delete it from the radix tree.
+ * Otherwise some cached pages of an orphan old workgroup
+ * could be still linked after the new one is available.
+ */
+ if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
+ erofs_workgroup_unfreeze(grp, 1);
+ return false;
+ }
+
+ /*
+ * it is 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);
+
+ /*
+ * if managed cache is enable, the last refcount
+ * should indicate the related workstation.
+ */
+ erofs_workgroup_unfreeze_final(grp);
+ return true;
+}
+#else
/* for nocache case, no customized reclaim path at all */
static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
struct erofs_workgroup *grp,
@@ -165,7 +212,7 @@ static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
erofs_workgroup_put(grp);
return true;
}
-
+#endif

unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
unsigned long nr_shrink,
@@ -312,3 +359,58 @@ void erofs_exit_shrinker(void)

#endif

+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+static const struct address_space_operations managed_cache_aops;
+
+struct inode *erofs_init_managed_cache(struct super_block *sb)
+{
+ struct inode *const inode = new_inode(sb);
+
+ if (unlikely(!inode))
+ return NULL;
+
+ 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);
+ return inode;
+}
+
+static int erofs_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 erofs_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 (!erofs_managed_cache_releasepage(page, GFP_NOFS))
+ cond_resched();
+}
+
+static const struct address_space_operations managed_cache_aops = {
+ .releasepage = erofs_managed_cache_releasepage,
+ .invalidatepage = erofs_managed_cache_invalidatepage,
+};
+#endif
+
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index a3e4de0f9c64..7bf25efae53c 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -162,6 +162,118 @@ struct z_erofs_decompress_frontend {
static struct page *z_pagemap_global[Z_EROFS_VMAP_GLOBAL_PAGES];
static DEFINE_MUTEX(z_pagemap_global_lock);

+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+static void preload_compressed_pages(struct z_erofs_collector *clt,
+ struct address_space *mc,
+ enum z_erofs_cache_alloctype type,
+ struct list_head *pagepool)
+{
+ 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' */
+ 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) {
+ pcl->compressed_pages[i] = NULL;
+ ret = 1;
+ break;
+ }
+ }
+ erofs_workgroup_unfreeze(&pcl->obj, 1);
+
+ if (ret) {
+ ClearPagePrivate(page);
+ put_page(page);
+ }
+ }
+ return ret;
+}
+#else
static void preload_compressed_pages(struct z_erofs_collector *clt,
struct address_space *mc,
enum z_erofs_cache_alloctype type,
@@ -169,6 +281,7 @@ static void preload_compressed_pages(struct z_erofs_collector *clt,
{
/* nowhere to load compressed pages from */
}
+#endif

/* page_type must be Z_EROFS_PAGE_TYPE_EXCLUSIVE */
static inline bool try_inplace_io(struct z_erofs_collector *clt,
@@ -440,6 +553,13 @@ static inline struct page *__stagingpage_alloc(struct list_head *pagepool,
static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
erofs_off_t la)
{
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ if (fe->backmost)
+ return true;
+#if (EROFS_FS_HAS_MANAGED_CACHE >= 2)
+ return la < fe->headoffset;
+#endif
+#endif
return false;
}

@@ -1002,6 +1122,9 @@ static struct z_erofs_unzip_io *jobqueue_init(struct super_block *sb,

/* define decompression jobqueue types */
enum {
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ JQ_BYPASS,
+#endif
JQ_SUBMIT,
NR_JOBQUEUES,
};
@@ -1012,12 +1135,56 @@ static void *jobqueueset_init(struct super_block *sb,
struct z_erofs_unzip_io *fgq,
bool forcefg)
{
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ /*
+ * 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;
+#endif
+
q[JQ_SUBMIT] = jobqueue_init(sb, fgq + JQ_SUBMIT, forcefg);
qtail[JQ_SUBMIT] = &q[JQ_SUBMIT]->head;

return tagptr_cast_ptr(tagptr_fold(tagptr1_t, q[JQ_SUBMIT], !forcefg));
}

+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+static void move_to_bypass_jobqueue(struct z_erofs_pcluster *pcl,
+ z_erofs_next_pcluster_t qtail[],
+ z_erofs_next_pcluster_t owned_head)
+{
+ 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)
+{
+ /*
+ * 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;
+}
+#else
static void move_to_bypass_jobqueue(struct z_erofs_pcluster *pcl,
z_erofs_next_pcluster_t qtail[],
z_erofs_next_pcluster_t owned_head)
@@ -1034,6 +1201,7 @@ static bool postsubmit_is_all_bypassed(struct z_erofs_unzip_io *q[],
DBG_BUGON(!nr_bios);
return false;
}
+#endif

static bool z_erofs_vle_submit_all(struct super_block *sb,
z_erofs_next_pcluster_t owned_head,
@@ -1145,6 +1313,9 @@ static void z_erofs_submit_and_unzip(struct super_block *sb,
pagepool, io, force_fg))
return;

+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ z_erofs_vle_unzip_all(sb, &io[JQ_BYPASS], pagepool);
+#endif
if (!force_fg)
return;

diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
index d07a7aa9a1a8..1e89dcea6b93 100644
--- a/fs/erofs/zdata.h
+++ b/fs/erofs/zdata.h
@@ -101,9 +101,18 @@ struct z_erofs_unzip_io_sb {
struct super_block *sb;
};

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

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