Introduce a dynamic minimum to dsk_reserve_chunks ...

... such that the total reserve is no less than 2MB.

This is required for stable operation of LRU when the log is full.

Ref #28

src/fellow_tune.c

@@ -92,6 +92,18 @@ stvfe_tune_check(struct stvfe_tune *tune)
 		tune->mem_reserve_chunks = l;
 	}
 
+	// 2MB
+	if (tune->chunk_exponent < 21U) {
+		l = 1U << (21U - tune->chunk_exponent);
+		if (tune->dsk_reserve_chunks < l) {
+			fprintf(stderr,"fellow: dsk_reserve_chunks raised from "
+			    "%u to %u (x %zu) for minimum size of 2MB\n",
+			    tune->dsk_reserve_chunks, l,
+			    (size_t)1 << tune->chunk_exponent);
+			tune->dsk_reserve_chunks = l;
+		}
+	}
+
 	sz = tune->dsksz >> (tune->chunk_exponent + 3);
 	assert(sz <= UINT_MAX);
 	l = (unsigned)sz;

src/vmod_slash.man.rst

@@ -612,7 +612,7 @@ fellow storage can be fine tuned:
 
   - unit: scalar
   - default: 4
-  - minimum: 2
+  - minimum: 2 MB / chunk_bytes
   - maximum: dsksize / 8 / chunk_bytes
 
   specifies a number of chunks to reserve on disk. The reserve is used
@@ -623,6 +623,9 @@ fellow storage can be fine tuned:
   fixed log space is full, might momentarily require additional space
   before making room.
 
+  The value is always raised to a dynamic minimum such that the disk
+  reserve is at least 2MB.
+
   The value is capped suck that the number of reserved chunks times
   the chunk size does not exceed 1/8 of the disk size.
 

src/vmod_slash.vcc

@@ -548,7 +548,7 @@ fellow storage can be fine tuned:
 
   - unit: scalar
   - default: 4
-  - minimum: 2
+  - minimum: 2 MB / chunk_bytes
   - maximum: dsksize / 8 / chunk_bytes
 
   specifies a number of chunks to reserve on disk. The reserve is used
@@ -559,6 +559,9 @@ fellow storage can be fine tuned:
   fixed log space is full, might momentarily require additional space
   before making room.
 
+  The value is always raised to a dynamic minimum such that the disk
+  reserve is at least 2MB.
+
   The value is capped suck that the number of reserved chunks times
   the chunk size does not exceed 1/8 of the disk size.
 

src/vtc/fellow_global.vtc

@@ -230,10 +230,6 @@ client c5 -repeat 1 {
 	rxresp
 	expect resp.status == 200
 	expect resp.body == ""
-	txreq -url "/tune" -hdr "dsk-reserve-chunks: 1"
-	rxresp
-	expect resp.status == 400
-	expect resp.body == "Value of dsk_reserve_chunks is too small, minimum is 2"
 } -start
 
 client c6 -repeat 1 {

src/vtc/fellow_global_shared.vtc

@@ -235,10 +235,6 @@ client c5 -repeat 1 {
 	rxresp
 	expect resp.status == 200
 	expect resp.body == ""
-	txreq -url "/tune" -hdr "dsk-reserve-chunks: 1"
-	rxresp
-	expect resp.status == 400
-	expect resp.body == "Value of dsk_reserve_chunks is too small, minimum is 2"
 } -start
 
 client c6 -repeat 1 {

src/vtc/fellow_vcl.vtc

@@ -238,10 +238,6 @@ client c5 -repeat 1 {
 	rxresp
 	expect resp.status == 200
 	expect resp.body == ""
-	txreq -url "/tune" -hdr "dsk-reserve-chunks: 1"
-	rxresp
-	expect resp.status == 400
-	expect resp.body == "Value of dsk_reserve_chunks is too small, minimum is 2"
 } -start
 
 client c6 -repeat 1 {