shithub: gefs

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blk: async sync

allow enqueuing new writes while we wait for the blocks
in queue to hit disk, so that our write throughput doesn't
drop dramatically when syncing.

--- a/blk.c

+++ b/blk.c

@@ -482,7 +482,7 @@

 }

 int

-syncbarrier(Arena *a, vlong gen)

+logbarrier(Arena *a, vlong gen)

 {

 	logappend(a, gen<<8, 0, LogSync);

 	if(a->loghd.addr == -1)

@@ -1076,12 +1076,33 @@

 	}

 }

+vlong

+wrbarrier(void)

+{

+	Qent qe;

+	vlong gen;

+	int i;

+	

+	gen = aincv(&fs->qgen, 1);

+	fs->syncing = fs->nsyncers;

+	for(i = 0; i < fs->nsyncers; i++){

+		qe.op = Qfence;

+		qe.bp.addr = 0;

+		qe.bp.hash = -1;

+		qe.bp.gen = -1;

+		qe.b = nil;

+		qput(&fs->syncq[i], qe);

+	}

+	while(fs->syncing != 0)

+		rsleep(&fs->syncrz);

+	return gen;

+}

+

 void

 sync(void)

 {

 	uvlong gen;

 	Arena *a;

-	Qent qe;

 	int i;

@@ -1098,25 +1119,14 @@

 		nexterror();

 	}

 	flushdlcache(1);

-	gen = aincv(&fs->qgen, 1);

-	fs->syncing = fs->nsyncers;

-	for(i = 0; i < fs->nsyncers; i++){

-		qe.op = Qfence;

-		qe.bp.addr = 0;

-		qe.bp.hash = -1;

-		qe.bp.gen = -1;

-		qe.b = nil;

-		qput(&fs->syncq[i], qe);

-	}

-	while(fs->syncing != 0)

-		rsleep(&fs->syncrz);

+	gen = wrbarrier();

 	/* pass 0: sync arena contents */

 	for(i = 0; i < fs->narena; i++){

 		a = &fs->arenas[i];

 		qlock(a);

-		syncbarrier(a, gen);

-		finalize(a->logtl);

-		syncblk(a->logtl);

+		logbarrier(a, gen);

+		setflag(a->logtl, Bdirty);

+		enqueue(a->logtl);

 		qunlock(a);

 	}

 	/*

@@ -1128,10 +1138,11 @@

 		a = &fs->arenas[i];

 		qlock(a);

 		packarena(a->h0->data, Blksz, a);

-		finalize(a->h0);

-		syncblk(a->h0);

+		setflag(a->h0, Bdirty);

+		enqueue(a->h0);

 		qunlock(a);

 	}

+	wrbarrier();

 	/*

 	 * pass 2: sync superblock; we have a consistent

 	 * set of block headers, so if we crash, we can

@@ -1157,8 +1168,8 @@

 		a = &fs->arenas[i];

 		qlock(a);

 		packarena(a->h1->data, Blksz, a);

-		finalize(a->h1);

-		syncblk(a->h1);

+		setflag(a->h1, Bdirty);

+		enqueue(a->h1);

 		qunlock(a);

 	}

 	/*

--- a/fs.c

+++ b/fs.c

@@ -2256,10 +2256,10 @@

 			for(mnt = fs->mounts; mnt != nil; mnt = mnt->next)

 				updatesnap(&mnt->root, mnt->root, mnt->name);

 			unlock(&fs->mountlk);

-			sync();

+			qunlock(&fs->mutlk);

 			epochend(id);

 			epochclean();

-			qunlock(&fs->mutlk);

+			sync();

 			for(i = 0; i < fs->narena; i++){

 				for(bp = oldhd[i]; bp.addr != -1; bp = nb){