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Subject[PATCH 01/10] mm: pagecache add lock
Date
Add a per address space lock around adding pages to the pagecache - making it
possible for fallocate INSERT_RANGE/COLLAPSE_RANGE to work correctly, and also
hopefully making truncate and dio a bit saner.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
---
fs/inode.c | 1 +
include/linux/fs.h | 23 +++++++++++
include/linux/sched.h | 4 ++
init/init_task.c | 1 +
mm/filemap.c | 91 ++++++++++++++++++++++++++++++++++++++++---
5 files changed, 115 insertions(+), 5 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index ef362364d3..e7aaa39adb 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -350,6 +350,7 @@ void address_space_init_once(struct address_space *mapping)
{
memset(mapping, 0, sizeof(*mapping));
INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC | __GFP_ACCOUNT);
+ pagecache_lock_init(&mapping->add_lock);
spin_lock_init(&mapping->tree_lock);
init_rwsem(&mapping->i_mmap_rwsem);
INIT_LIST_HEAD(&mapping->private_list);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c6baf76761..18d2886a44 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -388,9 +388,32 @@ int pagecache_write_end(struct file *, struct address_space *mapping,
loff_t pos, unsigned len, unsigned copied,
struct page *page, void *fsdata);

+/*
+ * Two-state lock - can be taken for add or block - both states are shared,
+ * like read side of rwsem, but conflict with other state:
+ */
+struct pagecache_lock {
+ atomic_long_t v;
+ wait_queue_head_t wait;
+};
+
+static inline void pagecache_lock_init(struct pagecache_lock *lock)
+{
+ atomic_long_set(&lock->v, 0);
+ init_waitqueue_head(&lock->wait);
+}
+
+void pagecache_add_put(struct pagecache_lock *);
+void pagecache_add_get(struct pagecache_lock *);
+void __pagecache_block_put(struct pagecache_lock *);
+void __pagecache_block_get(struct pagecache_lock *);
+void pagecache_block_put(struct pagecache_lock *);
+void pagecache_block_get(struct pagecache_lock *);
+
struct address_space {
struct inode *host; /* owner: inode, block_device */
struct radix_tree_root page_tree; /* radix tree of all pages */
+ struct pagecache_lock add_lock; /* protects adding new pages */
spinlock_t tree_lock; /* and lock protecting it */
atomic_t i_mmap_writable;/* count VM_SHARED mappings */
struct rb_root_cached i_mmap; /* tree of private and shared mappings */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b161ef8a90..e58465f61a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -40,6 +40,7 @@ struct io_context;
struct mempolicy;
struct nameidata;
struct nsproxy;
+struct pagecache_lock;
struct perf_event_context;
struct pid_namespace;
struct pipe_inode_info;
@@ -865,6 +866,9 @@ struct task_struct {
unsigned int in_ubsan;
#endif

+ /* currently held lock, for avoiding recursing in fault path: */
+ struct pagecache_lock *pagecache_lock;
+
/* Journalling filesystem info: */
void *journal_info;

diff --git a/init/init_task.c b/init/init_task.c
index 3ac6e754cf..308d46eef9 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -106,6 +106,7 @@ struct task_struct init_task
},
.blocked = {{0}},
.alloc_lock = __SPIN_LOCK_UNLOCKED(init_task.alloc_lock),
+ .pagecache_lock = NULL,
.journal_info = NULL,
INIT_CPU_TIMERS(init_task)
.pi_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
diff --git a/mm/filemap.c b/mm/filemap.c
index 693f62212a..31dd888785 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -111,6 +111,73 @@
* ->tasklist_lock (memory_failure, collect_procs_ao)
*/

+static void __pagecache_lock_put(struct pagecache_lock *lock, long i)
+{
+ BUG_ON(atomic_long_read(&lock->v) == 0);
+
+ if (atomic_long_sub_return_release(i, &lock->v) == 0)
+ wake_up_all(&lock->wait);
+}
+
+static bool __pagecache_lock_tryget(struct pagecache_lock *lock, long i)
+{
+ long v = atomic_long_read(&lock->v), old;
+
+ do {
+ old = v;
+
+ if (i > 0 ? v < 0 : v > 0)
+ return false;
+ } while ((v = atomic_long_cmpxchg_acquire(&lock->v,
+ old, old + i)) != old);
+ return true;
+}
+
+static void __pagecache_lock_get(struct pagecache_lock *lock, long i)
+{
+ wait_event(lock->wait, __pagecache_lock_tryget(lock, i));
+}
+
+void pagecache_add_put(struct pagecache_lock *lock)
+{
+ __pagecache_lock_put(lock, 1);
+}
+EXPORT_SYMBOL(pagecache_add_put);
+
+void pagecache_add_get(struct pagecache_lock *lock)
+{
+ __pagecache_lock_get(lock, 1);
+}
+EXPORT_SYMBOL(pagecache_add_get);
+
+void __pagecache_block_put(struct pagecache_lock *lock)
+{
+ __pagecache_lock_put(lock, -1);
+}
+EXPORT_SYMBOL(__pagecache_block_put);
+
+void __pagecache_block_get(struct pagecache_lock *lock)
+{
+ __pagecache_lock_get(lock, -1);
+}
+EXPORT_SYMBOL(__pagecache_block_get);
+
+void pagecache_block_put(struct pagecache_lock *lock)
+{
+ BUG_ON(current->pagecache_lock != lock);
+ current->pagecache_lock = NULL;
+ __pagecache_lock_put(lock, -1);
+}
+EXPORT_SYMBOL(pagecache_block_put);
+
+void pagecache_block_get(struct pagecache_lock *lock)
+{
+ __pagecache_lock_get(lock, -1);
+ BUG_ON(current->pagecache_lock);
+ current->pagecache_lock = lock;
+}
+EXPORT_SYMBOL(pagecache_block_get);
+
static int page_cache_tree_insert(struct address_space *mapping,
struct page *page, void **shadowp)
{
@@ -834,18 +901,21 @@ static int __add_to_page_cache_locked(struct page *page,
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageSwapBacked(page), page);

+ if (current->pagecache_lock != &mapping->add_lock)
+ pagecache_add_get(&mapping->add_lock);
+
if (!huge) {
error = mem_cgroup_try_charge(page, current->mm,
gfp_mask, &memcg, false);
if (error)
- return error;
+ goto err;
}

error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
if (error) {
if (!huge)
mem_cgroup_cancel_charge(page, memcg, false);
- return error;
+ goto err;
}

get_page(page);
@@ -865,7 +935,11 @@ static int __add_to_page_cache_locked(struct page *page,
if (!huge)
mem_cgroup_commit_charge(page, memcg, false, false);
trace_mm_filemap_add_to_page_cache(page);
- return 0;
+err:
+ if (current->pagecache_lock != &mapping->add_lock)
+ pagecache_add_put(&mapping->add_lock);
+
+ return error;
err_insert:
page->mapping = NULL;
/* Leave page->index set: truncation relies upon it */
@@ -873,7 +947,7 @@ static int __add_to_page_cache_locked(struct page *page,
if (!huge)
mem_cgroup_cancel_charge(page, memcg, false);
put_page(page);
- return error;
+ goto err;
}

/**
@@ -2511,7 +2585,14 @@ int filemap_fault(struct vm_fault *vmf)
* Do we have something in the page cache already?
*/
page = find_get_page(mapping, offset);
- if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
+ if (unlikely(current->pagecache_lock == &mapping->add_lock)) {
+ /*
+ * fault from e.g. dio -> get_user_pages() - _don't_ want to do
+ * readahead, only read in page we need:
+ */
+ if (!page)
+ goto no_cached_page;
+ } else if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
/*
* We found the page, so try async readahead before
* waiting for the lock.
--
2.17.0
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