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newfs_msdos: align data area to VM page boundary by default

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Without alignment, the data area will not be aligned with the buffer
cache, leading to overhead, higher write multiplication on SSD devices
and issues with very large cluster sizes (see PR 277414).

The -A option used to align the start of the root directory to a
multiple of the cluster size, which happens to align the start of the
data area with a buffer page boundary in case of large clusters and
the default number of directory entries (512 entries requiring 16 KB
for FAT12 or FAT16, FAT32 puts the root directory into the data area).

This commit aligns the start of the data area with the page size, if
neither -A nor -r is used. It changes -A to align the start of the
data area (end of the root directory) to a multiple of the cluster
size, since this is the alignment that prevents write multiplication
due to clusters crossing erase block boundaries of a SSD device.
The -r option is unchanged and will prevent any automatic alignment
from occuring.

Approved by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D45436
This commit is contained in:
Stefan Eßer 2024-06-02 14:07:52 +02:00
parent e461c7bc7d
commit 077f757d72
2 changed files with 32 additions and 10 deletions
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26
sbin/newfs_msdos/mkfs_msdos.c
View File

@ -249,7 +249,7 @@ mkfs_msdos(const char *fname, const char *dtype, const struct msdos_options *op)
ssize_t n;
time_t now;
u_int fat, bss, rds, cls, dir, lsn, x, x1, x2;
u_int extra_res, alignment, saved_x, attempts=0;
u_int extra_res, alignment, alignto, saved_x, attempts=0;
bool set_res, set_spf, set_spc;
int fd, fd1, rv;
struct msdos_options o = *op;
@ -412,8 +412,12 @@ mkfs_msdos(const char *fname, const char *dtype, const struct msdos_options *op)
}
bpb.bpbFATs = o.num_FAT;
}
if (o.directory_entries)
bpb.bpbRootDirEnts = o.directory_entries;
if (o.directory_entries) {
bpb.bpbRootDirEnts = roundup(o.directory_entries,
bpb.bpbBytesPerSec / sizeof(struct de));
if (bpb.bpbBytesPerSec == 0 || o.directory_entries >= MAXU16)
bpb.bpbRootDirEnts = MAXU16;
}
if (o.media_descriptor_set) {
if (o.media_descriptor < 0xf0) {
warnx("illegal media descriptor (%#x)", o.media_descriptor);
@ -564,14 +568,20 @@ mkfs_msdos(const char *fname, const char *dtype, const struct msdos_options *op)
x1 += (bpb.bpbBigFATsecs - 1) * bpb.bpbFATs;
}
if (set_res) {
/* attempt to align root directory */
alignment = (bpb.bpbResSectors + bpb.bpbBigFATsecs * bpb.bpbFATs) %
bpb.bpbSecPerClust;
if (o.align)
extra_res += bpb.bpbSecPerClust - alignment;
alignto = bpb.bpbSecPerClust;
else
alignto = PAGE_SIZE / bpb.bpbBytesPerSec;
if (alignto > 1) {
/* align data clusters */
alignment = (bpb.bpbResSectors + bpb.bpbBigFATsecs * bpb.bpbFATs + rds) %
alignto;
if (alignment != 0)
extra_res += alignto - alignment;
}
}
attempts++;
} while (o.align && alignment != 0 && attempts < 2);
} while (alignment != 0 && attempts < 2);
if (o.align && alignment != 0)
warnx("warning: Alignment failed.");

16
sbin/newfs_msdos/newfs_msdos.8
View File

@ -23,7 +23,7 @@
.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
.\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd January 12, 2024
.Dd June 2, 2024
.Dt NEWFS_MSDOS 8
.Os
.Sh NAME
@ -91,7 +91,13 @@ A suffix s, k, m, g (lower or upper case)
appended to the offset specifies that the
number is in sectors, kilobytes, megabytes or gigabytes, respectively.
.It Fl A
Attempt to cluster align root directory, useful for SD card.
Attempt to cluster align the data area, useful for SD card.
If neither the
.Fl A
nor
.Fl r
option is used, the number of reserved sectors is set to a value that aligns
the start of the data area to a multiple of the page size of the host.
.It Fl B Ar boot
Get bootstrap from file.
.It Fl C Ar create-size
@ -167,6 +173,12 @@ is 2.
Number of hidden sectors.
.It Fl r Ar reserved
Number of reserved sectors.
If neither the
.Fl A
nor
.Fl r
option is used, the number of reserved sectors is set to a value that aligns
the start of the data area to a multiple of the page size of the host.
.It Fl s Ar total
File system size.
.It Fl u Ar track-size