fellow_log: Extend memsz check to shared memory cache

Each fellow storage reserves a minimum amount of memory.

Closes #51

src/buddy.c

@@ -1385,6 +1385,8 @@ BUDDYF(init_)(unsigned witness, buddy_t *buddy, unsigned min, size_t size,
 
 	for (u = 0; u <= BUDDY_WAIT_MAXPRI; u++)
 		VTAILQ_INIT(&buddy->reqs_head[u]);
+
+	buddy->rsv_avail = size;
 }
 
 void

src/buddy.h

@@ -62,6 +62,8 @@ struct BUDDY {
 	pthread_mutex_t	minfo_mtx;
 	struct buddy_minfo_head minfo_head;
 
+	size_t			rsv_avail;
+
 	// under map_mtx
 	size_t			deficit;
 	unsigned		waiting;
@@ -161,6 +163,17 @@ BUDDYF(rndup)(const buddy_t *buddy, size_t sz)
 	return (rup_min(sz, map->min));
 }
 
+static inline size_t
+BUDDYF(reserve)(buddy_t *buddy, size_t sz)
+{
+
+	CHECK_OBJ_NOTNULL(buddy, BUDDY_MAGIC);
+	if (sz > buddy->rsv_avail)
+		sz = buddy->rsv_avail;
+	buddy->rsv_avail -= sz;
+	return (sz);
+}
+
 /* shall be defined as the larger of intptr_t and off_t */
 typedef off_t buddyoff_t;
 

src/fellow_log.c

@@ -6362,7 +6362,7 @@ fellow_log_init(const char *path, size_t wantsize, size_t objsz_hint,
 	struct stat			st;
 	unsigned			i;
 	unsigned			entries;
-	size_t				sz;
+	size_t				sz, got;
 	int32_t				ssz;
 	uint64_t			objsize = 0;
 	char				last_err[256] = "";
@@ -6523,19 +6523,25 @@ fellow_log_init(const char *path, size_t wantsize, size_t objsz_hint,
 		    path, ffd->active_hdr, ffd->log_info.generation);
 	}
 
-	if (objsize > MIN_FELLOW_BLOCK)
-		sz = MEMBUDDY_MINSIZE(wantsize, objsize);
-	else
-		sz = 0;
+	if (objsize < MIN_FELLOW_BLOCK)
+		objsize = objsz_hint;
+
+	sz = MEMBUDDY_MINSIZE(wantsize, objsize);
 
-	if (buddy_size(membuddy) < sz) {
-		ffd->diag("\nfellow:\tFATAL: memsz too small for "
-		    "actual objsize %zu < objsize_hint %zu!\n"
-		    "fellow:\tlower objsize_hint to %s or "
-		    "increase memsz to %s and restart.\n",
-		    (size_t)objsize, objsz_hint,
-		    pow2_unit(log2down(objsize)),
-		    pow2_unit(log2up(sz)));
+	if ((got = buddy_reserve(membuddy, sz)) < sz) {
+		ffd->diag("\nfellow:\tFATAL:\tfailed reserve of "
+		    "minimum memory size %zu.\n", sz);
+		if (objsize < objsz_hint) {
+			ffd->diag("fellow:\t\tactual objsize %zu "
+			    "< objsize_hint %zu.\n",
+			    (size_t)objsize, objsz_hint);
+			ffd->diag("fellow:\t\tlower objsize_hint to %s or ",
+			    pow2_unit(log2down(objsize)));
+		}
+		else
+			ffd->diag("fellow:\t\t");
+		ffd->diag("increase memsz by %s and restart.\n",
+		    pow2_unit(log2up(sz - got)));
 		goto err_close;
 	}
 

src/vmod_slash.vcc

@@ -222,9 +222,9 @@ argument.
 Memory Cache Sharing
 ~~~~~~~~~~~~~~~~~~~~
 
-When memory cache sharing with the ``<memsize>[=<storage>]``
-syntax is configured, *<memsize>* is used for sanity checking
-only. The actual memory size is always that of the referenced storage.
+When memory cache sharing with the ``<memsize>[=<storage>]`` syntax is
+configured, *<memsize>* is ignored. The actual memory size is always
+that of the referenced storage.
 
 LRU with memory cache sharing is cooperative. Whenever memory is
 needed by any storage, all storages using the shared cache are asked
@@ -417,10 +417,16 @@ actual figures are output at startup as ``fellow: metadata (bitmap)
 memory``.
 
 *objsize_hint* (default 256KB) is used to sanity check *memsize* in
-relation to *dsksize*. It should be set to a value lower than the
-average object size (actual or expected). If *memsize* is configured
-too low with respect to *dsksize* and *objsize_hint*, a higher value
-will be used (which might fail of insufficient memory is available).
+relation to *dsksize* and to size the fixed log regions. It should be
+set to a value **lower** than the expected average object size. If
+*memsize* is configured too low with respect to *dsksize* and
+*objsize_hint*, a higher *memsize* value will be used (which might
+fail if insufficient memory is available).
+
+For an already populated storage, the configured *memsize* is checked
+against the minimum amount of memory required for the actual average
+object size. If it is too low, fellow will not start and emit a fatal
+error with sizing requirements.
 
 *delete* specifies if the storage is to be emptied.