[PATCH 3/5] xlog: allow to limit number of files deleted by xdir_collect_garbage

[Vladimir Davydov <vdavydov.dev@gmail.com>]

Add an extra argument to xdir_collect_garbage() that specifies the max
number of files to delete. It will be used to delete old WAL files one
by one when running out of disk space.

Needed for #3397
---
 src/box/memtx_engine.c |  2 +-
 src/box/vy_log.c       |  2 +-
 src/box/wal.c          |  2 +-
 src/box/xlog.c         | 13 ++++++++++---
 src/box/xlog.h         |  8 +++++++-
 5 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/box/memtx_engine.c b/src/box/memtx_engine.c
index ae1f5a0e..04dc052b 100644
--- a/src/box/memtx_engine.c
+++ b/src/box/memtx_engine.c
@@ -834,7 +834,7 @@ memtx_engine_collect_garbage(struct engine *engine, int64_t lsn)
 	 * That said, we have to abort garbage collection if we
 	 * fail to delete a snap file.
 	 */
-	if (xdir_collect_garbage(&memtx->snap_dir, lsn, true) != 0)
+	if (xdir_collect_garbage(&memtx->snap_dir, lsn, -1, true) < 0)
 		return -1;
 
 	return 0;
diff --git a/src/box/vy_log.c b/src/box/vy_log.c
index fc8ede59..bb454eaa 100644
--- a/src/box/vy_log.c
+++ b/src/box/vy_log.c
@@ -1078,7 +1078,7 @@ vy_log_collect_garbage(int64_t signature)
 	 * it is still needed for backups.
 	 */
 	signature = vy_log_prev_checkpoint(signature);
-	xdir_collect_garbage(&vy_log.dir, signature, true);
+	xdir_collect_garbage(&vy_log.dir, signature, -1, true);
 }
 
 int64_t
diff --git a/src/box/wal.c b/src/box/wal.c
index 91c16fb0..2728318a 100644
--- a/src/box/wal.c
+++ b/src/box/wal.c
@@ -538,7 +538,7 @@ static int
 wal_collect_garbage_f(struct cbus_call_msg *data)
 {
 	int64_t lsn = ((struct wal_gc_msg *)data)->lsn;
-	xdir_collect_garbage(&wal_writer_singleton.wal_dir, lsn, false);
+	xdir_collect_garbage(&wal_writer_singleton.wal_dir, lsn, -1, false);
 	return 0;
 }
 
diff --git a/src/box/xlog.c b/src/box/xlog.c
index 292c462c..1a6ead7f 100644
--- a/src/box/xlog.c
+++ b/src/box/xlog.c
@@ -669,10 +669,16 @@ xdir_format_filename(struct xdir *dir, int64_t signature,
 }
 
 int
-xdir_collect_garbage(struct xdir *dir, int64_t signature, bool use_coio)
+xdir_collect_garbage(struct xdir *dir, int64_t signature,
+		     int max_files, bool use_coio)
 {
+	if (max_files <= 0)
+		max_files = INT_MAX;
+
+	int count = 0;
 	struct vclock *vclock;
-	while ((vclock = vclockset_first(&dir->index)) != NULL &&
+	while (count < max_files &&
+	       (vclock = vclockset_first(&dir->index)) != NULL &&
 	       vclock_sum(vclock) < signature) {
 		char *filename = xdir_format_filename(dir, vclock_sum(vclock),
 						      NONE);
@@ -694,8 +700,9 @@ xdir_collect_garbage(struct xdir *dir, int64_t signature, bool use_coio)
 			say_info("removed %s", filename);
 		vclockset_remove(&dir->index, vclock);
 		free(vclock);
+		count++;
 	}
-	return 0;
+	return count;
 }
 
 void
diff --git a/src/box/xlog.h b/src/box/xlog.h
index f9243935..2233c022 100644
--- a/src/box/xlog.h
+++ b/src/box/xlog.h
@@ -180,10 +180,16 @@ xdir_format_filename(struct xdir *dir, int64_t signature,
 
 /**
  * Remove files whose signature is less than specified.
+ * If @max_files > 0, stop after deleting @max_files files.
  * If @use_coio is set, files are deleted by coio threads.
+ *
+ * On success, this function returns the number of deleted
+ * files. If it failed to delete a file, it returns -1 and
+ * sets diag.
  */
 int
-xdir_collect_garbage(struct xdir *dir, int64_t signature, bool use_coio);
+xdir_collect_garbage(struct xdir *dir, int64_t signature,
+		     int max_files, bool use_coio);
 
 /**
  * Remove inprogress files in the specified directory.
-- 
2.11.0