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 <ptesarik@xxxxxxxx>
---
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.ptesarik@xxxxxxxx>
In-Reply-To: <5e0004648d2a597417542b483a0c3aed114bf03f.1523636414.git.ptesarik@xxxxxxxx>
References: <5e0004648d2a597417542b483a0c3aed114bf03f.1523636414.git.ptesarik@xxxxxxxx>
From: Petr Tesarik <ptesarik@xxxxxxx>
Date: Fri, 13 Apr 2018 17:35:55 +0200
Subject: [PATCH 2/2] Check PG_swapbacked for swap cache pages
To: Masaki Tachibana <mas-tachibana@xxxxxxxxxxxxx>,
Takuya Nakayama <tak-nakayama@xxxxxxxxxxxxx>,
kexec-ml <kexec@xxxxxxxxxxxxxxxxxxx>
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
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