POSIX_FADV_NOREUSE is now supported in Linux. Update text regarding former no op behavior. Indicate the readahead policy and treatment of file pages read with this flag. Link: <https://lore.kernel.org/linux-mm/20221230215252.2628425-2-yuzhao@xxxxxxxxxx/> Signed-off-by: T.J. Alumbaugh <talumbau@xxxxxxxxxx> Signed-off-by: Yuanchu Xie <yuanchu@xxxxxxxxxx> --- Changelog v5 -> v6 - Fixed wordiness - Clarified LRU to mean the kernel page replacement algorithm v4 -> v5 - Remove unnecessary changes - Use two space inter-sentence spacing - Fix lines exceeding 80-column v3 -> v4 - Use semantic newlines - Format with macros like .B instead of inline \f v3: https://lore.kernel.org/linux-man/20230320222057.1976956-1-talumbau@xxxxxxxxxx/ v4: https://lore.kernel.org/linux-man/20241113031654.3964740-1-yuanchu@xxxxxxxxxx/ v5: https://lore.kernel.org/linux-man/20241114012233.4152152-1-yuanchu@xxxxxxxxxx/ man/man2/posix_fadvise.2 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/man/man2/posix_fadvise.2 b/man/man2/posix_fadvise.2 index ed40b0c0d..894a0762c 100644 --- a/man/man2/posix_fadvise.2 +++ b/man/man2/posix_fadvise.2 @@ -64,7 +64,13 @@ The specified data will be accessed only once. .IP Before Linux 2.6.18, \fBPOSIX_FADV_NOREUSE\fP had the same semantics as \fBPOSIX_FADV_WILLNEED\fP. -This was probably a bug; since Linux 2.6.18, this flag is a no-op. +This was probably a bug; +from Linux 2.6.18 until Linux 6.2 this flag was a no-op. +Since Linux 6.3, +.B POSIX_FADV_NOREUSE +signals that the kernel page replacement algorithm +can ignore access to mapped page cache marked by this flag. +This is useful, for example, while streaming large files. .TP .B POSIX_FADV_WILLNEED The specified data will be accessed in the near future. @@ -130,6 +136,8 @@ in this case.) Under Linux, \fBPOSIX_FADV_NORMAL\fP sets the readahead window to the default size for the backing device; \fBPOSIX_FADV_SEQUENTIAL\fP doubles this size, and \fBPOSIX_FADV_RANDOM\fP disables file readahead entirely. +.B POSIX_FADV_NOREUSE +does not modify the readahead window size. These changes affect the entire file, not just the specified region (but other open file handles to the same file are unaffected). .SS C library/kernel differences -- 2.46.0
