docs: explain type of memory allocated by md_per_io_size

Note that md_per_io_size always uses malloc for io_uring_cmd. Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
axboe · Nov 22, 2024 · dc03e37 · dc03e37
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diff --git a/HOWTO.rst b/HOWTO.rst
@@ -2591,7 +2591,9 @@ with the caveat that when used on the command line, they must come after the
 
 .. option:: md_per_io_size=int : [io_uring_cmd] [xnvme]
 
-	Size in bytes for separate metadata buffer per IO. Default: 0.
+        Size in bytes for separate metadata buffer per IO. For io_uring_cmd
+        these buffers are allocated using malloc regardless of what is set for
+        :option:`iomem`. Default: 0.
 
 .. option:: pi_act=int : [io_uring_cmd] [xnvme]
 

diff --git a/fio.1 b/fio.1
@@ -2361,7 +2361,9 @@ this option is specified, the option \fBplids\fP or \fBfdp_pli\fP will be ignore
 .RE
 .TP
 .BI (io_uring_cmd,xnvme)md_per_io_size \fR=\fPint
-Size in bytes for separate metadata buffer per IO. Default: 0.
+Size in bytes for separate metadata buffer per IO. For io_uring_cmd these
+buffers are allocated using malloc regardless of what is set for \fBiomem\fR.
+Default: 0.
 .TP
 .BI (io_uring_cmd,xnvme)pi_act \fR=\fPint
 Action to take when nvme namespace is formatted with protection information.