shithub: clone

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Fix directory read serialization bottleneck

The directory walker used dirreadall call for loading directory
entries into memory before assigning them to workers -- causing
severe and unwanted serialization that was especially noticeable
on long directories.

The solution is simple: chunk up the directory read and assign
work in between the chunks.

--- a/clone.c

+++ b/clone.c

@@ -263,32 +263,29 @@

 		error("can't open: %r");

 		return;

 	}

-	n = dirreadall(fd, &dirs);

-	if(n < 0){

-		error("can't read directory: %r");

-		close(fd);

-		return;

-	}

-	close(fd);

-

-	for(d = dirs; n; n--, d++){

-		if(d->mode & DMDIR && same(skipdir, d))

-			continue;

-

-		sn = smprint("%s/%s", src, d->name);

-		dn = smprint("%s/%s", dst, d->name);

-		if(d->mode & DMDIR){

-			if(mkdir(sn, dn, d, nil) < 0)

+	while((n = dirread(fd, &dirs)) > 0){

+		for(d = dirs; n; n--, d++){

+			if(d->mode & DMDIR && same(skipdir, d))

 				continue;

-			clonedir(sn, dn);

-		}else{

-			f = filenew(sn, dn, d);

-			sendp(filechan, f);

+

+			sn = smprint("%s/%s", src, d->name);

+			dn = smprint("%s/%s", dst, d->name);

+			if(d->mode & DMDIR){

+				if(mkdir(sn, dn, d, nil) < 0)

+					continue;

+				clonedir(sn, dn);

+			}else{

+				f = filenew(sn, dn, d);

+				sendp(filechan, f);

+			}

+			free(sn);

+			free(dn);

 		}

-		free(sn);

-		free(dn);

+		free(dirs);

 	}

-	free(dirs);

+	if(n < 0)

+		error("can't read directory: %r");

+	close(fd);

 }

 void