From e88aee660ea668cc96d8a5a11060b6e02b2f0fd7 Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Wed, 17 Jul 2024 17:00:19 +0200
Subject: kernel: actually store the tag (and size) in the kmalloc metadata

I'm storing more information in less space. Win-win.
---
 src/kernel/malloc.c | 64 ++++++++++++++++++++++++++++-------------------------
 1 file changed, 34 insertions(+), 30 deletions(-)

(limited to 'src/kernel/malloc.c')

diff --git a/src/kernel/malloc.c b/src/kernel/malloc.c
index ca44cfe..9f87274 100644
--- a/src/kernel/malloc.c
+++ b/src/kernel/malloc.c
@@ -6,29 +6,27 @@
 #include <stdbool.h>
 #include <stdint.h>
 
-#define DESCLEN 8
-
 #define SCMIN  6 /* 1<<6  == 64 */
 #define SCMAX 12 /* 1<<11 == 2048 */
 
-const char *tagnames[] = {
-	"TagInvalid",
-	"TagKernelFs",
-	"TagProcFs",
-	"TagUserFs",
-	"TagOpenPath",
-	"TagMountPath",
-	"TagMountUser",
-	"TagMountRoot",
-	"TagExecbuf",
-	"TagVfsReq",
-	"TagHandleset",
-	"TagHandle",
-	"TagProcess",
-	"TagProcessHandle",
-	"TagDevTime",
-	"TagRootCache",
-	"TagPageRefcount",
+static const char *tagnames[] = {
+	"Invalid", /* TagInvalid */
+	"KernelFs", /* TagKernelFs */
+	"ProcFs", /* TagProcFs */
+	"UserFs", /* TagUserFs */
+	"OpenPath", /* TagOpenPath */
+	"MountPath", /* TagMountPath */
+	"MountUser", /* TagMountUser */
+	"MountRoot", /* TagMountRoot */
+	"Execbuf", /* TagExecbuf */
+	"VfsReq", /* TagVfsReq */
+	"Handleset", /* TagHandleset */
+	"Handle", /* TagHandle */
+	"Process", /* TagProcess */
+	"ProcessHandle", /* TagProcessHandle */
+	"DevTime", /* TagDevTime */
+	"RootCache", /* TagRootCache */
+	"PageRefcount", /* TagPageRefcount */
 };
 static_assert(sizeof(tagnames) == sizeof(const char *) * TagLast);
 
@@ -46,6 +44,14 @@ struct Slab {
 /* The code assumes the header fits within the first region. */
 static_assert(sizeof(Slab) <= 1<<SCMIN);
 
+/* stored at the end of a region */
+typedef struct AllocHdr AllocHdr;
+struct AllocHdr {
+	uint16_t len : 10;
+	uint16_t tag : 6;
+};
+static_assert(sizeof(AllocHdr) == 2); /* just making sure */
+
 /* Yes, I'm wasting a bit of memory here. */
 static Slab *freeslabs[SCMAX] = {NULL};
 static Slab *fullslabs[SCMAX] = {NULL};
@@ -76,7 +82,7 @@ crawllist(Slab *al, int sizeclass, bool full)
 	int regsize = 1ull << sizeclass;
 	for (; al; al = al->next) {
 		kprintf(
-			"%08p %016llx %s %d\n",
+			"%08p %016llx %s %db \n",
 			al, al->bitmap, full ? "full" : "part", 1ull<<al->sizeclass
 		);
 
@@ -88,8 +94,10 @@ crawllist(Slab *al, int sizeclass, bool full)
 
 		for (int i = 1; i * regsize < PAGE_SIZE; i++) {
 			char *p = ((char*)al) + i * regsize;
+			AllocHdr *hdr = (void*)p + regsize - sizeof(AllocHdr);
 			if (al->bitmap & (1ull<<i)) {
-				kprintf("%08p %.8s\n", p, p + regsize - DESCLEN);
+				assert(hdr->tag != TagInvalid && hdr->tag < TagLast);
+				kprintf("%08p %4db %s\n", p, hdr->len, tagnames[hdr->tag]);
 			}
 		}
 	}
@@ -137,10 +145,8 @@ kmalloc(size_t len, enum MallocTag tag)
 	uint64_t idx;
 
 	assert(tag != TagInvalid && tag < TagLast);
-	const char *desc = tagnames[tag] + 3; // very temporary
-
 	assert(len <= KMALLOC_MAX);
-	len += DESCLEN;
+	len += sizeof(AllocHdr);
 	sizeclass = getsizeclass(len);
 	regsize = 1ull << sizeclass;
 
@@ -162,11 +168,9 @@ kmalloc(size_t len, enum MallocTag tag)
 	ret = ((char*)al) + regsize * idx;
 	al->bitmap |= 1ull<<idx;
 
-	char *descloc = ret + regsize - DESCLEN;
-	memset(descloc, ' ', DESCLEN);
-	for (int i = 0; i < DESCLEN && desc[i]; i++) {
-		descloc[i] = desc[i];
-	}
+	AllocHdr *hdr = ret + regsize - sizeof(AllocHdr);
+	hdr->len = len - sizeof(AllocHdr);
+	hdr->tag = tag;
 
 	/* if this was the last free region, move to fullslabs */
 	if (isfull(al->bitmap, sizeclass)) {
-- 
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