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gefs: skip writeback on data blocks

when writing back data blocks, we didn't
read the data back from disk, and instead
just enqueued the block pointer; This means
that we don't have the Blk struct to set
the freed flag on, so we would commit every
IO operation to a data block.

This change opportunistically reaches into
the cache and flags the data block as dead,
so we can skip writeback.

--- a/sys/src/cmd/gefs/blk.c

+++ b/sys/src/cmd/gefs/blk.c

@@ -937,6 +937,7 @@

 			qe.bp = p->bp;

 			qe.b = nil;

 			qput(a->sync, qe);

+			cacheflag(p->bp.addr, Bfreed);

 			if(p->b != nil){

 				clrflag(p->b, Blimbo);

 				setflag(p->b, Bfreed);

--- a/sys/src/cmd/gefs/cache.c

+++ b/sys/src/cmd/gefs/cache.c

@@ -137,6 +137,25 @@

 	qunlock(&fs->lrulk);

 }

+void

+cacheflag(vlong addr, int flg)

+{

+	Bucket *bkt;

+	u32int h;

+	Blk *b;

+

+	h = ihash(addr);

+	bkt = &fs->bcache[h % fs->cmax];

+	qlock(&fs->lrulk);

+	lock(bkt);

+	for(b = bkt->b; b != nil; b = b->hnext)

+		if(b->bp.addr == addr)

+			setflag(b, flg);

+	unlock(bkt);

+	qunlock(&fs->lrulk);

+

+}

+

 Blk*

 cacheget(vlong addr)

 {

--- a/sys/src/cmd/gefs/fns.h

+++ b/sys/src/cmd/gefs/fns.h

@@ -47,6 +47,7 @@

 void	lrubot(Blk*);

 void	cacheins(Blk*);

 void	cachedel(vlong);

+void	cacheflag(vlong, int);

 Blk*	cacheget(vlong);

 Blk*	cachepluck(void);

-- 

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