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author | Rick Macklem <rmacklem@FreeBSD.org> | 2021-01-03 01:21:21 +0000 |
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committer | Rick Macklem <rmacklem@FreeBSD.org> | 2021-01-03 01:21:21 +0000 |
commit | d189a74dfdcd4a89c92a48ecbf8fcb6f6903f9b6 (patch) | |
tree | d24792d2a5dc9fa3fec2768746b98857632f24c0 /lib | |
parent | c98a764c681f8b70812a9f13a6e61c96aa1a69d2 (diff) | |
download | src-d189a74dfdcd4a89c92a48ecbf8fcb6f6903f9b6.tar.gz src-d189a74dfdcd4a89c92a48ecbf8fcb6f6903f9b6.zip |
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
Diffstat (limited to 'lib')
-rw-r--r-- | lib/libc/sys/copy_file_range.2 | 11 |
1 files changed, 10 insertions, 1 deletions
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 |