Re: [PATCH v1 3/3] xfs_io: Add RWF_DONTCACHE support to preadv2

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

"Darrick J. Wong" <djwong@kernel.org> writes:

> On Tue, Mar 04, 2025 at 05:25:37PM +0530, Ritesh Harjani (IBM) wrote:
>> Add per-io RWF_DONTCACHE support flag to preadv2()
>> This enables xfs_io to perform buffered-io read which can drop the page
>> cache folios after reading.
>> 
>> 	e.g. xfs_io -c "pread -U -V 1 0 16K" /mnt/f1
>> 
>> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>> ---
>>  io/pread.c        | 12 ++++++++++--
>>  man/man8/xfs_io.8 |  8 +++++++-
>>  2 files changed, 17 insertions(+), 3 deletions(-)
>> 
>> diff --git a/io/pread.c b/io/pread.c
>> index 782f2a36..64c28784 100644
>> --- a/io/pread.c
>> +++ b/io/pread.c
>> @@ -38,6 +38,9 @@ pread_help(void)
>>  " -Z N -- zeed the random number generator (used when reading randomly)\n"
>>  "         (heh, zorry, the -s/-S arguments were already in use in pwrite)\n"
>>  " -V N -- use vectored IO with N iovecs of blocksize each (preadv)\n"
>> +#ifdef HAVE_PWRITEV2
>
> HAVE_PREADV2?
>

Thanks for catching that. Will fix this in v2.

-ritesh

> --D
>
>> +" -U   -- Perform the preadv2() with Uncached/RWF_DONTCACHE\n"
>> +#endif
>>  "\n"
>>  " When in \"random\" mode, the number of read operations will equal the\n"
>>  " number required to do a complete forward/backward scan of the range.\n"
>> @@ -388,7 +391,7 @@ pread_f(
>>  	init_cvtnum(&fsblocksize, &fssectsize);
>>  	bsize = fsblocksize;
>>  
>> -	while ((c = getopt(argc, argv, "b:BCFRquvV:Z:")) != EOF) {
>> +	while ((c = getopt(argc, argv, "b:BCFRquUvV:Z:")) != EOF) {
>>  		switch (c) {
>>  		case 'b':
>>  			tmp = cvtnum(fsblocksize, fssectsize, optarg);
>> @@ -417,6 +420,11 @@ pread_f(
>>  		case 'u':
>>  			uflag = 1;
>>  			break;
>> +#ifdef HAVE_PREADV2
>> +		case 'U':
>> +			preadv2_flags |= RWF_DONTCACHE;
>> +			break;
>> +#endif
>>  		case 'v':
>>  			vflag = 1;
>>  			break;
>> @@ -514,7 +522,7 @@ pread_init(void)
>>  	pread_cmd.argmin = 2;
>>  	pread_cmd.argmax = -1;
>>  	pread_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
>> -	pread_cmd.args = _("[-b bs] [-qv] [-i N] [-FBR [-Z N]] off len");
>> +	pread_cmd.args = _("[-b bs] [-qUv] [-i N] [-FBR [-Z N]] off len");
>>  	pread_cmd.oneline = _("reads a number of bytes at a specified offset");
>>  	pread_cmd.help = pread_help;
>>  
>> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
>> index 47af5232..df508054 100644
>> --- a/man/man8/xfs_io.8
>> +++ b/man/man8/xfs_io.8
>> @@ -200,7 +200,7 @@ option will set the file permissions to read-write (0644). This allows xfs_io to
>>  set up mismatches between the file permissions and the open file descriptor
>>  read/write mode to exercise permission checks inside various syscalls.
>>  .TP
>> -.BI "pread [ \-b " bsize " ] [ \-qv ] [ \-FBR [ \-Z " seed " ] ] [ \-V " vectors " ] " "offset length"
>> +.BI "pread [ \-b " bsize " ] [ \-qUv ] [ \-FBR [ \-Z " seed " ] ] [ \-V " vectors " ] " "offset length"
>>  Reads a range of bytes in a specified blocksize from the given
>>  .IR offset .
>>  .RS 1.0i
>> @@ -214,6 +214,12 @@ requests will be split. The default blocksize is 4096 bytes.
>>  .B \-q
>>  quiet mode, do not write anything to standard output.
>>  .TP
>> +.B \-U
>> +Perform the
>> +.BR preadv2 (2)
>> +call with
>> +.IR RWF_DONTCACHE .
>> +.TP
>>  .B \-v
>>  dump the contents of the buffer after reading,
>>  by default only the count of bytes actually read is dumped.
>> -- 
>> 2.48.1
>> 
>>