When page cache is filtered out (dump level bitmap includes 2 or 4), makedumpfile checks the PG_swapcache bit, but since kernel commit 6326fec1122cde256bd2a8c63f2606e08e44ce1d (v4.10-rc1~7) this bit is an alias for PG_owner_priv_1, which is also used by filesystem code (PG_checked) and Xen (PG_pinned and PG_foreign). With these kernels, the PG_swapcache flag is valid only if PG_swapbacked is set. A Linux kernel patch has already been submitted to export the value of PG_swapbacked in VMCOREINFO. Since there are released kernels in the wild which do not export the value, a fallback is implemented. I considered these three situations: 1. Kernels before v2.6.28-rc1~244: PG_swapbacked does not exist, so it must not be checked. Instead, check PG_swapcache, which is never overloaded for another purpose. 2. Kernels between v2.6.28-rc1~244 and v4.10-rc1~7: It is sufficient to check only PG_swapcache, but PG_swapbacked may also be checked (it is always set if PG_swapcache is set). 3. Kernels since v4.10-rc1~7: PG_swapbacked must be checked. If PG_swapbacked value is known (exported or read from debuginfo), it is always safe to use it (case 2 or 3). If PG_swapbacked is not known, it is safe to ignore it for cases 1 and 2, but not 3. Thankfully, the new value of PG_swapcache (since v4.10-rc1~7) is less than PG_private (which is known), whereas the old value had always been greater than PG_private. Moreover, the flags between PG_private and PG_swapbacked haven't changed since v4.10-rc1~7, so PG_swapbacked can fall back to PG_private + 6 if unknown. Without this patch, all Xen dumps are unusable, because PG_pinned is set for all page table pages. Signed-off-by: Petr Tesarik <ptesarik@xxxxxxxx> --- makedumpfile.c | 19 ++++++++++++++++++- makedumpfile.h | 2 ++ 2 files changed, 20 insertions(+), 1 deletion(-) diff --git a/makedumpfile.c b/makedumpfile.c index 175ba68..ec04a88 100644 --- a/makedumpfile.c +++ b/makedumpfile.c @@ -252,7 +252,18 @@ isHugetlb(unsigned long dtor) static int is_cache_page(unsigned long flags) { - return isLRU(flags) || isSwapCache(flags); + if (isLRU(flags)) + return TRUE; + + /* PG_swapcache is valid only if: + * a. PG_swapbacked bit is set, or + * b. PG_swapbacked did not exist (kernels before 4.10-rc1). + */ + if ((NUMBER(PG_swapbacked) == NOT_FOUND_NUMBER || isSwapBacked(flags)) + && isSwapCache(flags)) + return TRUE; + + return FALSE; } static inline unsigned long @@ -1735,6 +1746,7 @@ get_structure_info(void) ENUM_NUMBER_INIT(PG_lru, "PG_lru"); ENUM_NUMBER_INIT(PG_private, "PG_private"); ENUM_NUMBER_INIT(PG_swapcache, "PG_swapcache"); + ENUM_NUMBER_INIT(PG_swapbacked, "PG_swapbacked"); ENUM_NUMBER_INIT(PG_buddy, "PG_buddy"); ENUM_NUMBER_INIT(PG_slab, "PG_slab"); ENUM_NUMBER_INIT(PG_hwpoison, "PG_hwpoison"); @@ -1988,6 +2000,9 @@ get_value_for_old_linux(void) NUMBER(PG_private) = PG_private_ORIGINAL; if (NUMBER(PG_swapcache) == NOT_FOUND_NUMBER) NUMBER(PG_swapcache) = PG_swapcache_ORIGINAL; + if (NUMBER(PG_swapbacked) == NOT_FOUND_NUMBER + && NUMBER(PG_swapcache) < NUMBER(PG_private)) + NUMBER(PG_swapbacked) = NUMBER(PG_private) + 6; if (NUMBER(PG_slab) == NOT_FOUND_NUMBER) NUMBER(PG_slab) = PG_slab_ORIGINAL; if (NUMBER(PG_head_mask) == NOT_FOUND_NUMBER) @@ -2264,6 +2279,7 @@ write_vmcoreinfo_data(void) WRITE_NUMBER("PG_private", PG_private); WRITE_NUMBER("PG_head_mask", PG_head_mask); WRITE_NUMBER("PG_swapcache", PG_swapcache); + WRITE_NUMBER("PG_swapbacked", PG_swapbacked); WRITE_NUMBER("PG_buddy", PG_buddy); WRITE_NUMBER("PG_slab", PG_slab); WRITE_NUMBER("PG_hwpoison", PG_hwpoison); @@ -2658,6 +2674,7 @@ read_vmcoreinfo(void) READ_NUMBER("PG_private", PG_private); READ_NUMBER("PG_head_mask", PG_head_mask); READ_NUMBER("PG_swapcache", PG_swapcache); + READ_NUMBER("PG_swapbacked", PG_swapbacked); READ_NUMBER("PG_slab", PG_slab); READ_NUMBER("PG_buddy", PG_buddy); READ_NUMBER("PG_hwpoison", PG_hwpoison); diff --git a/makedumpfile.h b/makedumpfile.h index 6205ef3..fe306bb 100644 --- a/makedumpfile.h +++ b/makedumpfile.h @@ -155,6 +155,7 @@ test_bit(int nr, unsigned long addr) #define isPrivate(flags) test_bit(NUMBER(PG_private), flags) #define isCompoundHead(flags) (!!((flags) & NUMBER(PG_head_mask))) #define isSwapCache(flags) test_bit(NUMBER(PG_swapcache), flags) +#define isSwapBacked(flags) test_bit(NUMBER(PG_swapbacked), flags) #define isHWPOISON(flags) (test_bit(NUMBER(PG_hwpoison), flags) \ && (NUMBER(PG_hwpoison) != NOT_FOUND_NUMBER)) @@ -1881,6 +1882,7 @@ struct number_table { long PG_head; long PG_head_mask; long PG_swapcache; + long PG_swapbacked; long PG_buddy; long PG_slab; long PG_hwpoison; -- 2.13.6 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec