Previously, the buffer for LVM metadata parsing was set to twice the
size of the metadata area, which caused excessive memory use.
This patch changes the allocation to read the actual raw metadata blocks
directly from the metadata area. Instead of using twice the entire
metadata area size, we now allocate just what’s needed for the raw
metadata.
To illustrate, We can determine the size of the LVM metadata area by
running the command:
pvs -o pv_name,pv_mda_size
As a result, grub will allocate 2 * pv_mda_size, and since 1MiB is a
common default for pv_mda_size nowadays (it seems), this results in 2MiB
being allocated.
However, most of the blocks in the metadata area are not useful to grub.
A lot of space gets wasted because it is occupied by a pre-allocated
circular buffer, which is used to track changes over time. To eliminate
this overhead, we can teach grub to use the raw metadata block to locate
the active metadata within the circular buffer.
This change effectively reduces the buffer size while still working
correctly. In my test system on openSUSE, the buffer size for LVM
metadata dropped from 2,088,960 bytes to 1,119 bytes, which is a big
improvement.
Signed-off-by: Michael Chang <mch...@suse.com>
---
grub-core/disk/lvm.c | 79 ++++++++++++++++++++++++--------------------
1 file changed, 43 insertions(+), 36 deletions(-)
diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 0c32c95f9..ea260b47e 100644
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -140,9 +140,11 @@ grub_lvm_detect (grub_disk_t disk,
grub_err_t err;
grub_uint64_t mda_offset, mda_size;
grub_size_t ptr;
+ grub_uint64_t mda_raw_offset, mda_raw_size;
char buf[GRUB_LVM_LABEL_SIZE];
char vg_id[GRUB_LVM_ID_STRLEN+1];
char pv_id[GRUB_LVM_ID_STRLEN+1];
+ char mdah_buf[sizeof (struct grub_lvm_mda_header) + sizeof (struct
grub_lvm_raw_locn)];
char *metadatabuf, *mda_end, *vgname;
const char *p, *q;
struct grub_lvm_label_header *lh = (struct grub_lvm_label_header *) buf;
@@ -220,21 +222,15 @@ grub_lvm_detect (grub_disk_t disk,
dlocn++;
mda_offset = grub_le_to_cpu64 (dlocn->offset);
- mda_size = grub_le_to_cpu64 (dlocn->size);
/* It's possible to have multiple copies of metadata areas, we just use the
first one. */
-
- /* Allocate buffer space for the circular worst-case scenario. */
- metadatabuf = grub_calloc (2, mda_size);
- if (! metadatabuf)
+ err = grub_disk_read (disk, 0, mda_offset, sizeof (mdah_buf), mdah_buf);
+ if (err)
goto fail;
- err = grub_disk_read (disk, 0, mda_offset, mda_size, metadatabuf);
- if (err)
- goto fail2;
+ mdah = (struct grub_lvm_mda_header *) mdah_buf;
- mdah = (struct grub_lvm_mda_header *) metadatabuf;
if ((grub_strncmp ((char *)mdah->magic, GRUB_LVM_FMTT_MAGIC,
sizeof (mdah->magic)))
|| (grub_le_to_cpu32 (mdah->version) != GRUB_LVM_FMTT_VERSION))
@@ -244,42 +240,58 @@ grub_lvm_detect (grub_disk_t disk,
#ifdef GRUB_UTIL
grub_util_info ("unknown LVM metadata header");
#endif
- goto fail2;
+ goto fail;
}
rlocn = mdah->raw_locns;
- if (grub_le_to_cpu64 (rlocn->offset) >= grub_le_to_cpu64 (mda_size))
+
+ mda_size = grub_le_to_cpu64 (mdah->size);
+ mda_raw_size = grub_le_to_cpu64 (rlocn->size);
+ mda_raw_offset = grub_le_to_cpu64 (rlocn->offset);
+
+ if (mda_raw_offset >= mda_size)
{
#ifdef GRUB_UTIL
grub_util_info ("metadata offset is beyond end of metadata area");
#endif
- goto fail2;
+ goto fail;
}
- if (grub_le_to_cpu64 (rlocn->offset) + grub_le_to_cpu64 (rlocn->size) >
- grub_le_to_cpu64 (mdah->size))
+ metadatabuf = grub_malloc (mda_raw_size);
+
+ if (! metadatabuf)
+ goto fail;
+
+ if (mda_raw_offset + mda_raw_size > mda_size)
{
- if (2 * mda_size < GRUB_LVM_MDA_HEADER_SIZE ||
- (grub_le_to_cpu64 (rlocn->offset) + grub_le_to_cpu64 (rlocn->size) -
- grub_le_to_cpu64 (mdah->size) > mda_size - GRUB_LVM_MDA_HEADER_SIZE))
- {
-#ifdef GRUB_UTIL
- grub_util_info ("cannot copy metadata wrap in circular buffer");
-#endif
- goto fail2;
- }
+ err = grub_disk_read (disk, 0,
+ mda_offset + mda_raw_offset,
+ mda_size - mda_raw_offset,
+ metadatabuf);
+ if (err)
+ goto fail2;
/* Metadata is circular. Copy the wrap in place. */
- grub_memcpy (metadatabuf + mda_size,
- metadatabuf + GRUB_LVM_MDA_HEADER_SIZE,
- grub_le_to_cpu64 (rlocn->offset) +
- grub_le_to_cpu64 (rlocn->size) -
- grub_le_to_cpu64 (mdah->size));
+ err = grub_disk_read (disk, 0,
+ mda_offset + GRUB_LVM_MDA_HEADER_SIZE,
+ mda_raw_offset + mda_raw_size - mda_size,
+ metadatabuf + mda_size - mda_raw_offset);
+ if (err)
+ goto fail2;
+ }
+ else
+ {
+ err = grub_disk_read (disk, 0,
+ mda_offset + mda_raw_offset,
+ mda_raw_size,
+ metadatabuf);
+ if (err)
+ goto fail2;
}
- if (grub_add ((grub_size_t)metadatabuf,
- (grub_size_t)grub_le_to_cpu64 (rlocn->offset),
- &ptr))
+ p = q = metadatabuf;
+
+ if (grub_add ((grub_size_t)metadatabuf, (grub_size_t)mda_raw_size, &ptr))
{
error_parsing_metadata:
#ifdef GRUB_UTIL
@@ -288,11 +300,6 @@ grub_lvm_detect (grub_disk_t disk,
goto fail2;
}
- p = q = (char *)ptr;
-
- if (grub_add (ptr, (grub_size_t) grub_le_to_cpu64 (rlocn->size), &ptr))
- goto error_parsing_metadata;
-
mda_end = (char *)ptr;
while (*q != ' ' && q < mda_end)
--
2.46.1
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