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statx.2: Minor edits to Ira Weiny's 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk 2020-09-29 10:25:02 +02:00
parent 38ad6a8808
commit c9e6c5abc9
1 changed files with 16 additions and 10 deletions
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@ -464,22 +464,28 @@ against a cryptographic hash that covers the
entire file (e.g., via a Merkle tree). entire file (e.g., via a Merkle tree).
.TP .TP
.BR STATX_ATTR_DAX (since Linux 5.8) .BR STATX_ATTR_DAX (since Linux 5.8)
The file is in the DAX (cpu direct access) state. DAX state attempts to The file is in the DAX (cpu direct access) state.
DAX state attempts to
minimize software cache effects for both I/O and memory mappings of this file. minimize software cache effects for both I/O and memory mappings of this file.
It requires a file system which has been configured to support DAX. It requires a file system which has been configured to support DAX.
.PP .PP
DAX generally assumes all accesses are via cpu load / store instructions which DAX generally assumes all accesses are via CPU load / store instructions
can minimize overhead for small accesses, but may adversely affect cpu which can minimize overhead for small accesses,
utilization for large transfers. but may adversely affect CPU utilization for large transfers.
.PP .PP
File I/O is done directly to/from user-space buffers and memory mapped I/O may File I/O is done directly to/from user-space buffers and memory mapped I/O may
be performed with direct memory mappings that bypass kernel page cache. be performed with direct memory mappings that bypass the kernel page cache.
.PP .PP
While the DAX property tends to result in data being transferred synchronously, While the DAX property tends to result in data being transferred synchronously,
it does not give the same guarantees of O_SYNC where data and the necessary it does not give the same guarantees as the
metadata are transferred together. .B O_SYNC
flag (see
.BR open (2)),
where data and the necessary metadata are transferred together.
.PP .PP
A DAX file may support being mapped with the MAP_SYNC flag, which enables a A DAX file may support being mapped with the
.B MAP_SYNC
flag, which enables a
program to use CPU cache flush instructions to persist CPU store operations program to use CPU cache flush instructions to persist CPU store operations
without an explicit without an explicit
.BR fsync (2). .BR fsync (2).