>The PFN_EXCLUDED value is used to control at which point a run of
>zeros in the bitmap (zeros denote excluded pages) is large enough
>to warrant truncating the current output segment and to create a
>new output segment (containing non-excluded pages), in an ELF dump.
>
>If the run is smaller than PFN_EXCLUDED, then those excluded pages
>are still output in the ELF dump, for the current output segment.
>
>By using smaller values of PFN_EXCLUDED, the resulting dump file
>size can be made smaller by actually removing more excluded pages
>from the resulting dump file.
>
>This patch adds the command line option --exclude-threshold=<value>
>to indicate the threshold. The default is 256, the legacy value
>of PFN_EXCLUDED. The smallest value permitted is 1.
>
>Using an existing vmcore, this was tested by the following:
>
>% makedumpfile -E -d31 --exclude-threshold=256 -x vmlinux vmcore newvmcore256
>% makedumpfile -E -d31 --exclude-threshold=4 -x vmlinux vmcore newvmcore4
>
>I utilize -d31 in order to exclude as many page types as possible,
>resulting in a [significantly] smaller file sizes than the original
>vmcore.
>
>-rwxrwx--- 1 edevolde edevolde 4034564096 Jun 27 10:24 vmcore
>-rw------- 1 edevolde edevolde 119808156 Jul 6 13:01 newvmcore256
>-rw------- 1 edevolde edevolde 100811276 Jul 6 13:08 newvmcore4
>
>The use of smaller value of PFN_EXCLUDED increases the number of
>output segments (the 'Number of program headers' in the readelf
>output) in the ELF dump file.
How will you tune the value ? I'm not sure what is the benefit of the
tunable PFN_EXCLUDED. If there is no regression caused by too many PT_LOAD
entries, I think we can decide a concrete PFN_EXCLUDED.
The penalty for splitting PT_LOAD is the size of a PT_LOAD header,
so the best PFN_EXCLUDED is the minimum number which meets the condition
below:
(size of PT_LOAD header) < (PFN_EXCLUDED << PAGE_SIZE)
>% readelf -h vmcore
>ELF Header:
> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
> Class: ELF64
> Data: 2's complement, little endian
> Version: 1 (current)
> OS/ABI: UNIX - System V
> ABI Version: 0
> Type: CORE (Core file)
> Machine: Advanced Micro Devices X86-64
> Version: 0x1
> Entry point address: 0x0
> Start of program headers: 64 (bytes into file)
> Start of section headers: 0 (bytes into file)
> Flags: 0x0
> Size of this header: 64 (bytes)
> Size of program headers: 56 (bytes)
> Number of program headers: 6
> ^^^
> Size of section headers: 0 (bytes)
> Number of section headers: 0
> Section header string table index: 0
>
>% readelf -h newvmcore256
>ELF Header:
> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
> Class: ELF64
> Data: 2's complement, little endian
> Version: 1 (current)
> OS/ABI: UNIX - System V
> ABI Version: 0
> Type: CORE (Core file)
> Machine: Advanced Micro Devices X86-64
> Version: 0x1
> Entry point address: 0x0
> Start of program headers: 64 (bytes into file)
> Start of section headers: 0 (bytes into file)
> Flags: 0x0
> Size of this header: 64 (bytes)
> Size of program headers: 56 (bytes)
> Number of program headers: 18
> ^^^
> Size of section headers: 0 (bytes)
> Number of section headers: 0
> Section header string table index: 0
>
>% readelf -h newvmcore4
>ELF Header:
> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
> Class: ELF64
> Data: 2's complement, little endian
> Version: 1 (current)
> OS/ABI: UNIX - System V
> ABI Version: 0
> Type: CORE (Core file)
> Machine: Advanced Micro Devices X86-64
> Version: 0x1
> Entry point address: 0x0
> Start of program headers: 64 (bytes into file)
> Start of section headers: 0 (bytes into file)
> Flags: 0x0
> Size of this header: 64 (bytes)
> Size of program headers: 56 (bytes)
> Number of program headers: 244
> ^^^
> Size of section headers: 0 (bytes)
> Number of section headers: 0
> Section header string table index: 0
>
>The newvmcore4 has an even smaller file size than newvmcore256, with
>the small price being that there are now 244 rather than 18 segments
>in the dump file.
>
>And with a larger number of segments, loading both vmcore and newvmcore4
>into 'crash' resulted in identical outputs when run with the dmesg, ps,
>files, mount, and net sub-commands.
What about the processing speed of crash, is there no slow down ?
Thanks,
Atsushi Kumagai
>Signed-off-by: Eric DeVolder <eric.devolder at oracle.com>
>---
>v1: Posted 06jul2017 to kexec-tools mailing list
> - original
>---
> makedumpfile.c | 20 +++++++++++++++++---
> makedumpfile.h | 4 +++-
> 2 files changed, 20 insertions(+), 4 deletions(-)
>
>diff --git a/makedumpfile.c b/makedumpfile.c
>index e69b6df..940f64c 100644
>--- a/makedumpfile.c
>+++ b/makedumpfile.c
>@@ -7236,7 +7236,7 @@ get_loads_dumpfile_cyclic(void)
>
> /*
> * If the number of the contiguous pages to be excluded
>- * is 256 or more, those pages are excluded really.
>+ * is PFN_EXCLUDED or more, those pages are excluded really.
> * And a new PT_LOAD segment is created.
> */
> if (num_excluded >= PFN_EXCLUDED) {
>@@ -7352,7 +7352,7 @@ write_elf_pages_cyclic(struct cache_data *cd_header, struct cache_data *cd_page)
> continue;
> /*
> * If the number of the contiguous pages to be excluded
>- * is 255 or less, those pages are not excluded.
>+ * is less than PFN_EXCLUDED, those pages are not excluded.
> */
> } else if (num_excluded < PFN_EXCLUDED) {
> if ((pfn == pfn_end - 1) && frac_tail) {
>@@ -7370,7 +7370,7 @@ write_elf_pages_cyclic(struct cache_data *cd_header, struct cache_data *cd_page)
>
> /*
> * If the number of the contiguous pages to be excluded
>- * is 256 or more, those pages are excluded really.
>+ * is PFN_EXCLUDED or more, those pages are excluded really.
> * And a new PT_LOAD segment is created.
> */
> load.p_memsz = memsz;
>@@ -11007,6 +11007,7 @@ static struct option longopts[] = {
> {"splitblock-size", required_argument, NULL, OPT_SPLITBLOCK_SIZE},
> {"work-dir", required_argument, NULL, OPT_WORKING_DIR},
> {"num-threads", required_argument, NULL, OPT_NUM_THREADS},
>+ {"exclude-threshold", required_argument, NULL, OPT_PFN_EXCLUDE_THRESHOLD},
> {0, 0, 0, 0}
> };
>
>@@ -11044,6 +11045,14 @@ main(int argc, char *argv[])
> */
> info->flag_usemmap = MMAP_TRY;
>
>+ /*
>+ * A run of zeros in the bitmap (excluded pages) of less than
>+ * pfn_excluded_threshold in length will still be dumped. Runs greater
>+ * than or equal to pfn_excluded_threshold will result in the creation
>+ * of a new output segment, for ELF dumps.
>+ */
>+ info->pfn_exclude_threshold = 256;
>+
> info->block_order = DEFAULT_ORDER;
> message_level = DEFAULT_MSG_LEVEL;
> while ((opt = getopt_long(argc, argv, "b:cDd:eEFfg:hi:lpRvXx:", longopts,
>@@ -11163,6 +11172,11 @@ main(int argc, char *argv[])
> case OPT_NUM_THREADS:
> info->num_threads = MAX(atoi(optarg), 0);
> break;
>+ case OPT_PFN_EXCLUDE_THRESHOLD:
>+ info->pfn_exclude_threshold = strtoul(optarg, NULL, 0);
>+ if (0 == info->pfn_exclude_threshold)
>+ info->pfn_exclude_threshold = 1;
>+ break;
> case '?':
> MSG("Commandline parameter is invalid.\n");
> MSG("Try `makedumpfile --help' for more information.\n");
>diff --git a/makedumpfile.h b/makedumpfile.h
>index e32e567..33d3eb0 100644
>--- a/makedumpfile.h
>+++ b/makedumpfile.h
>@@ -216,7 +216,7 @@ isAnon(unsigned long mapping)
>
> #define BITPERBYTE (8)
> #define PGMM_CACHED (512)
>-#define PFN_EXCLUDED (256)
>+#define PFN_EXCLUDED (info->pfn_exclude_threshold)
> #define BUFSIZE (1024)
> #define BUFSIZE_FGETS (1500)
> #define BUFSIZE_BITMAP (4096)
>@@ -1139,6 +1139,7 @@ struct DumpInfo {
> long page_size; /* size of page */
> long page_shift;
> mdf_pfn_t max_mapnr; /* number of page descriptor */
>+ unsigned long pfn_exclude_threshold;
> unsigned long page_offset;
> unsigned long section_size_bits;
> unsigned long max_physmem_bits;
>@@ -2143,6 +2144,7 @@ struct elf_prstatus {
> #define OPT_SPLITBLOCK_SIZE OPT_START+14
> #define OPT_WORKING_DIR OPT_START+15
> #define OPT_NUM_THREADS OPT_START+16
>+#define OPT_PFN_EXCLUDE_THRESHOLD OPT_START+17
>
> /*
> * Function Prototype.
>--
>2.7.4
