No functional change, but clarify the purpose of checking isLRU()
and SwapCache(), and move the check to a single place.

Signed-off-by: Petr Tesarik <ptesa...@suse.com>
---
 makedumpfile.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index d685427..175ba68 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -249,6 +249,12 @@ isHugetlb(unsigned long dtor)
                     && (SYMBOL(free_huge_page) == dtor));
 }
 
+static int
+is_cache_page(unsigned long flags)
+{
+       return isLRU(flags) || isSwapCache(flags);
+}
+
 static inline unsigned long
 calculate_len_buf_out(long page_size)
 {
@@ -5868,7 +5874,7 @@ __exclude_unnecessary_pages(unsigned long mem_map,
                 * Exclude the non-private cache page.
                 */
                else if ((info->dump_level & DL_EXCLUDE_CACHE)
-                   && (isLRU(flags) || isSwapCache(flags))
+                   && is_cache_page(flags)
                    && !isPrivate(flags) && !isAnon(mapping)) {
                        pfn_counter = &pfn_cache;
                }
@@ -5876,7 +5882,7 @@ __exclude_unnecessary_pages(unsigned long mem_map,
                 * Exclude the cache page whether private or non-private.
                 */
                else if ((info->dump_level & DL_EXCLUDE_CACHE_PRI)
-                   && (isLRU(flags) || isSwapCache(flags))
+                   && is_cache_page(flags)
                    && !isAnon(mapping)) {
                        if (isPrivate(flags))
                                pfn_counter = &pfn_cache_private;
-- 
2.13.6


>From 2efa8f466177a492abbe0cb64046ec8cd8b8afdf Mon Sep 17 00:00:00 2001
Message-Id: 
<2efa8f466177a492abbe0cb64046ec8cd8b8afdf.1523636414.git.ptesa...@suse.com>
In-Reply-To: 
<5e0004648d2a597417542b483a0c3aed114bf03f.1523636414.git.ptesa...@suse.com>
References: 
<5e0004648d2a597417542b483a0c3aed114bf03f.1523636414.git.ptesa...@suse.com>
From: Petr Tesarik <ptesa...@suse.cz>
Date: Fri, 13 Apr 2018 17:35:55 +0200
Subject: [PATCH 2/2] Check PG_swapbacked for swap cache pages
To: Masaki Tachibana <mas-tachib...@vf.jp.nec.com>,
    Takuya Nakayama <tak-nakay...@tg.jp.nec.com>,
    kexec-ml <kexec@lists.infradead.org>

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 <ptesa...@suse.com>
---
 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


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