sfdisk: (--move-data) keep step size based on optimal I/O

The current implementation is too paranoid and tries to keep in
memory only data which are on disk too. It means very small step size
when move partition only a few sectors left/right.

This patch enlarge the buffer to at least 1MiB and aligned to optimal
I/O.

Addresses: https://github.com/karelzak/util-linux/issues/848
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/disk-utils/sfdisk.c b/disk-utils/sfdisk.c
index 80c92fb21178dbeb554077394272f51ac0356fc8..c8efb5280bf9bb19470aa890722b3c58a06c2c8c 100644 (file)
--- a/disk-utils/sfdisk.c
+++ b/disk-utils/sfdisk.c
@@ -370,7 +370,7 @@ static int move_partition_data(struct sfdisk *sf, size_t partno, struct fdisk_pa
        FILE *f = NULL;
        int ok = 0, fd, backward = 0;
        fdisk_sector_t nsectors, from, to, step, i;
-       size_t ss, step_bytes, cc;
+       size_t io, ss, step_bytes, cc;
        uintmax_t src, dst;
        int errsv;
 
@@ -399,7 +399,7 @@ static int move_partition_data(struct sfdisk *sf, size_t partno, struct fdisk_pa
 
        fd = fdisk_get_devfd(sf->cxt);
 
-       ss = fdisk_get_sector_size(sf->cxt);
+       /* set move direction and overlay */
        nsectors = fdisk_partition_get_size(orig_pa);
        from = fdisk_partition_get_start(orig_pa);
        to = fdisk_partition_get_start(pa);
@@ -411,22 +411,24 @@ static int move_partition_data(struct sfdisk *sf, size_t partno, struct fdisk_pa
                DBG(MISC, ul_debug("overlay between source and target"));
                backward = from < to;
                DBG(MISC, ul_debug(" copy order: %s", backward ? "backward" : "forward"));
+       }
 
-               step = from > to ? from - to : to - from;
-               if (step > nsectors)
-                       step = nsectors;
-       } else
-               step = nsectors;
+       /* set optimal step size -- nearest to 1MiB aligned to optimal I/O */
+       io = fdisk_get_optimal_iosize(sf->cxt);
+       ss = fdisk_get_sector_size(sf->cxt);
+       if (!io)
+               io = ss;
+       if (io < 1024 * 1024)
+               step_bytes = ((1024 * 1024) + io/2) / io * io;
+       else
+               step_bytes = io;
 
-       /* make step usable for malloc() */
-       if (step * ss > (getpagesize() * 256U))
-               step = (getpagesize() * 256) / ss;
+       step = step_bytes / ss;
 
        /* align the step (note that nsectors does not have to be power of 2) */
        while (nsectors % step)
                step--;
 
-       step_bytes = step * ss;
        DBG(MISC, ul_debug(" step: %ju (%zu bytes)", (uintmax_t)step, step_bytes));
 
 #if defined(POSIX_FADV_SEQUENTIAL) && defined(HAVE_POSIX_FADVISE)