--- /n/sources/plan9/sys/src/cmd/fossil/cache.c	Fri Apr 14 16:55:36 2023
+++ /sys/src/cmd/fossil/cache.c	Tue Jun 16 10:39:51 2026
@@ -609,6 +609,51 @@
 	return b;
 }
 
+void
+cachePrefetch(Cache *c, u32int addr)
+{
+	Block *b;
+	ulong h;
+
+	if(!diskCanPrefetch(c->disk))
+		return;
+
+	h = addr % c->hashSize;
+	qlock(&c->lk);
+	for(b = c->heads[h]; b != nil; b = b->next)
+		if(b->part == PartData && b->addr == addr)
+			break;
+	if(b != nil){
+		qunlock(&c->lk);
+		return;
+	}
+	b = cacheBumpBlock(c);
+	b->part = PartData;
+	b->addr = addr;
+	localToGlobal(addr, b->score);
+	b->next = c->heads[h];
+	c->heads[h] = b;
+	if(b->next != nil)
+		b->next->prev = &b->next;
+	b->prev = &c->heads[h];
+	qunlock(&c->lk);
+
+	bwatchLock(b);
+	qlock(&b->lk);
+	b->nlock = 1;
+
+	if(b->iostate == BioEmpty){
+		if(!readLabel(c, &b->l, addr)){
+			blockPut(b);
+			return;
+		}
+		blockSetIOState(b, BioLabel);
+	}
+	if(b->iostate == BioEmpty || b->iostate == BioLabel)
+		diskRead(c->disk, b);
+	blockPut(b);
+}
+
 /*
  * fetch a global (Venti) block from the memory cache.
  * if it's not there, load it, bumping some other block.
--- /n/sources/plan9/sys/src/cmd/fossil/disk.c	Mon Nov 14 16:09:31 2016
+++ /sys/src/cmd/fossil/disk.c	Tue Jun 16 10:39:51 2026
@@ -215,6 +215,17 @@
 	diskQueue(disk, b);
 }
 
+int
+diskCanPrefetch(Disk *disk)
+{
+	int ok;
+
+	qlock(&disk->lk);
+	ok = disk->nqueue < QueueSize - 16;
+	qunlock(&disk->lk);
+	return ok;
+}
+
 void
 diskWrite(Disk *disk, Block *b)
 {
--- /n/sources/plan9/sys/src/cmd/fossil/source.c	Mon Nov 14 16:09:31 2016
+++ /sys/src/cmd/fossil/source.c	Tue Jun 16 10:39:51 2026
@@ -822,6 +822,32 @@
 }
 
 void
+sourceReadAhead(Source *r, ulong bn, int n)
+{
+	Entry e;
+	Block *pb;
+	u32int addr;
+	int np, i0, k;
+
+	assert(sourceIsLocked(r));
+	if(!sourceGetEntry(r, &e))
+		return;
+	if(e.depth == 0)
+		return;
+	np = e.psize/VtScoreSize;
+	i0 = bn % np;
+	pb = _sourceBlock(r, bn, OReadOnly, 1, 0);
+	if(pb == nil)
+		return;
+	for(k = 0; k < n && i0+k < np; k++){
+		addr = globalToLocal(pb->data + (i0+k)*VtScoreSize);
+		if(addr != NilBlock)
+			cachePrefetch(r->fs->cache, addr);
+	}
+	blockPut(pb);
+}
+
+void
 sourceClose(Source *r)
 {
 	if(r == nil)
--- /n/sources/plan9/sys/src/cmd/fossil/file.c	Wed Apr  7 19:24:25 2021
+++ /sys/src/cmd/fossil/file.c	Tue Jun 16 10:39:51 2026
@@ -46,6 +46,10 @@
 static void fileRAccess(File*);
 static void fileWAccess(File*, char*);
 
+enum {
+	RAWINDOW = 16,
+};
+
 static File *
 fileAlloc(Fs *fs)
 {
@@ -589,6 +593,40 @@
 	return -1;
 }
 
+void
+fileReadAhead(File *f, vlong offset, int n, u32int *raexpect, u32int *ramax)
+{
+	Source *s;
+	int dsize;
+	u32int bn0, last, start, frontier;
+
+	if(fileIsDir(f))
+		return;
+	if(!fileRLock(f))
+		return;
+	if(!sourceLock(f->source, OReadOnly)){
+		fileRUnlock(f);
+		return;
+	}
+	s = f->source;
+	dsize = s->dsize;
+	bn0 = offset/dsize;
+	last = (offset+n-1)/dsize;
+	if(offset == 0 || bn0 == *raexpect){
+		frontier = last+RAWINDOW;
+		start = *ramax;
+		if(start < last+1)
+			start = last+1;
+		if(start <= frontier)
+			sourceReadAhead(s, start, frontier-start+1);
+		*ramax = frontier+1;
+	}else
+		*ramax = last+1;
+	*raexpect = last+1;
+	sourceUnlock(s);
+	fileRUnlock(f);
+}
+
 /*
  * Changes the file block bn to be the given block score.
  * Very sneaky.  Only used by flfmt.
--- /n/sources/plan9/sys/src/cmd/fossil/9p.c	Sat Nov 12 00:09:03 2016
+++ /sys/src/cmd/fossil/9p.c	Tue Jun 16 10:39:51 2026
@@ -556,8 +556,12 @@
 		n = dirRead(fid, data, count, m->t.offset);
 	else if(fid->qid.type & QTAUTH)
 		n = authRead(fid, data, count);
-	else
+	else{
 		n = fileRead(fid->file, data, count, m->t.offset);
+		if(n > 0)
+			fileReadAhead(fid->file, m->t.offset, n,
+				&fid->raexpect, &fid->ramax);
+	}
 	if(n < 0)
 		goto error;
 
--- /n/sources/plan9/sys/src/cmd/fossil/9fid.c	Mon Nov 14 16:09:31 2016
+++ /sys/src/cmd/fossil/9fid.c	Tue Jun 16 10:39:51 2026
@@ -75,6 +75,8 @@
 	fid->ref = 0;
 	fid->flags = 0;
 	fid->open = FidOCreate;
+	fid->raexpect = 0;
+	fid->ramax = 0;
 	assert(fid->fsys == nil);
 	assert(fid->file == nil);
 	fid->qid = (Qid){0, 0, 0};
--- /n/sources/plan9/sys/src/cmd/fossil/9.h	Mon Nov 14 16:09:31 2016
+++ /sys/src/cmd/fossil/9.h	Tue Jun 16 10:39:51 2026
@@ -107,6 +107,8 @@
 	int	open;
 	Fsys*	fsys;
 	File*	file;
+	u32int	raexpect;
+	u32int	ramax;
 	Qid	qid;
 	char*	uid;
 	char*	uname;
--- /n/sources/plan9/sys/src/cmd/fossil/fns.h	Mon Nov 14 16:09:31 2016
+++ /sys/src/cmd/fossil/fns.h	Tue Jun 16 10:39:51 2026
@@ -9,6 +9,7 @@
 int	sourceLock(Source*, int);
 char	*sourceName(Source *s);
 Source*	sourceOpen(Source*, ulong, int, int);
+void	sourceReadAhead(Source*, ulong, int);
 int	sourceRemove(Source*);
 Source*	sourceRoot(Fs*, u32int, int);
 int	sourceSetDirSize(Source*, ulong);
@@ -27,6 +28,7 @@
 Block*	cacheLocal(Cache*, int, u32int, int);
 Block*	cacheLocalData(Cache*, u32int, int, u32int, int, u32int);
 u32int	cacheLocalSize(Cache*, int);
+void	cachePrefetch(Cache*, u32int);
 int	readLabel(Cache*, Label*, u32int addr);
 
 Block*	blockCopy(Block*, u32int, u32int, u32int);
@@ -43,6 +45,7 @@
 
 Disk*	diskAlloc(int);
 int	diskBlockSize(Disk*);
+int	diskCanPrefetch(Disk*);
 int	diskFlush(Disk*);
 void	diskFree(Disk*);
 void	diskRead(Disk*, Block*);
--- /n/sources/plan9/sys/src/cmd/fossil/fs.h	Mon Nov 14 16:09:31 2016
+++ /sys/src/cmd/fossil/fs.h	Tue Jun 16 10:39:51 2026
@@ -60,6 +60,7 @@
 char	*fileName(File *f);
 File	*fileOpen(Fs*, char*);
 int	fileRead(File*, void *, int, vlong);
+void	fileReadAhead(File*, vlong, int, u32int*, u32int*);
 int	fileRemove(File*, char*);
 int	fileSetDir(File*, DirEntry*, char*);
 int	fileSetQidSpace(File*, u64int, u64int);