The branch main has been updated by rmacklem:
URL:
https://cgit.FreeBSD.org/src/commit/?id=d189a74dfdcd4a89c92a48ecbf8fcb6f6903f9b6
commit d189a74dfdcd4a89c92a48ecbf8fcb6f6903f9b6
Author: Rick Macklem <rmack...@freebsd.org>
AuthorDate: 2021-01-03 01:21:21 +0000
Commit: Rick Macklem <rmack...@freebsd.org>
CommitDate: 2021-01-03 01:21:21 +0000
copy_file_range(2): add recommendation to use large "len"
PR#252358 reported a serious performance problem w.r.t.
cp(1) when copying large non-sparse files.
This problem appears to have been caused by cp(1)
calling copy_file_range(2) with a small "len" argument.
This patch adds a recommendation to use a large "len"
value where possible, for performance reasons.
Reviewed by: asomers
Differential Revision: https://reviews.freebsd.org/D27935
---
lib/libc/sys/copy_file_range.2 | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/lib/libc/sys/copy_file_range.2 b/lib/libc/sys/copy_file_range.2
index a3f714f0e7e8..22106b397ef2 100644
--- a/lib/libc/sys/copy_file_range.2
+++ b/lib/libc/sys/copy_file_range.2
@@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd March 30, 2020
+.Dd January 2, 2021
.Dt COPY_FILE_RANGE 2
.Os
.Sh NAME
@@ -117,6 +117,15 @@ with
.Dv SEEK_DATA
arguments and this system call for the
data ranges found.
+.Pp
+For best performance, call
+.Fn copy_file_range
+with the largest
+.Fa len
+value possible.
+It is interruptible on most file systems,
+so there is no penalty for using very large len values, even SSIZE_MAX.
+.Pp
.Sh RETURN VALUES
If it succeeds, the call returns the number of bytes copied, which can be fewer
than
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