1.) The bitmap of vmcore file can be very big in the server kernel panic, such as over 256M. This patch uses mmap/madvise to improve the read speed of the bitmap in the non-FLAT_FORMAT code path. Use MADV_WILLNEED for madvise, it will trigger read ahead for reading the bitmap. 2.) Test. The files: vmlinux: 272M vmcore : 23G (bitmap_len: 4575985664) #cat ./commands.txt quit Before this patch: #echo 3 > /proc/sys/vm/drop_caches; #time ./crash -i ./commands.txt /root/t/vmlinux /root/t/vmcore > /dev/null 2>&1 ............................ real 0m55.217s user 0m15.114s sys 0m3.560s ............................ After this patch: #echo 3 > /proc/sys/vm/drop_caches; #time ./crash -i ./commands.txt /root/t/vmlinux /root/t/vmcore > /dev/null 2>&1 ............................ real 0m44.097s user 0m19.031s sys 0m1.620s ............................ Signed-off-by: Huang Shijie <shijie(a)os.amperecomputing.com&gt; --- v1 --> v2: Use MADV_WILLNEED for mmap, not MADV_SEQUENTIAL. --- diskdump.c | 39 ++++++++++++++++----------------------- 1 file changed, 16 insertions(+), 23 deletions(-) diff --git a/diskdump.c b/diskdump.c index ff1e9a3..102062b 100644 --- a/diskdump.c +++ b/diskdump.c @@ -724,10 +724,6 @@ restart: offset = (off_t)block_size * (1 + header->sub_hdr_size); - if ((dd->bitmap = malloc(bitmap_len)) == NULL) - error(FATAL, "%s: cannot malloc bitmap buffer\n", - DISKDUMP_VALID() ? "diskdump" : "compressed kdump"); - dd->dumpable_bitmap = calloc(bitmap_len, 1); if (CRASHDEBUG(8)) @@ -736,30 +732,23 @@ restart: (ulonglong)offset); if (FLAT_FORMAT()) { + if ((dd->bitmap = malloc(bitmap_len)) == NULL) + error(FATAL, "%s: cannot malloc bitmap buffer\n", + DISKDUMP_VALID() ? "diskdump" : "compressed kdump"); + if (!read_flattened_format(dd->dfd, offset, dd->bitmap, bitmap_len)) { error(INFO, "%s: cannot read memory bitmap\n", DISKDUMP_VALID() ? "diskdump" : "compressed kdump"); goto err; } } else { - if (lseek(dd->dfd, offset, SEEK_SET) == failed) { - error(INFO, "%s: cannot lseek memory bitmap\n", + dd->bitmap = mmap(NULL, bitmap_len, PROT_READ, + MAP_SHARED, dd->dfd, offset); + if (dd->bitmap == MAP_FAILED) + error(FATAL, "%s: cannot mmap bitmap buffer\n", DISKDUMP_VALID() ? "diskdump" : "compressed kdump"); - goto err; - } - bufptr = dd->bitmap; - len = bitmap_len; - while (len) { - bytes_read = read(dd->dfd, bufptr, len); - if (bytes_read <= 0) { - error(INFO, "%s: cannot read memory bitmap\n", - DISKDUMP_VALID() ? "diskdump" - : "compressed kdump"); - goto err; - } - len -= bytes_read; - bufptr += bytes_read; - } + + madvise(dd->bitmap, bitmap_len, MADV_WILLNEED); } if (dump_is_partial(header)) @@ -920,8 +909,12 @@ err: free(sub_header); if (sub_header_kdump) free(sub_header_kdump); - if (dd->bitmap) - free(dd->bitmap); + if (dd->bitmap) { + if (FLAT_FORMAT()) + free(dd->bitmap); + else + munmap(dd->bitmap, dd->bitmap_len); + } if (dd->dumpable_bitmap) free(dd->dumpable_bitmap); if (dd->notes_buf) -- 2.30.2