Hi
Sharing 3 changes for zram regarding swap cache handling. Please have a look.
Subject: [PATCH 1/3] zram, swap cache missing page tree offset
Subject: [PATCH 2/3] zram, swap cache entries are pointer to struct page
Subject: [PATCH 3/3] zram, exclude shadow entries from swap cache lookup
Thanks
Johan
From 7cc73ed60d78fc173acc9367884561f3cdee9fab Mon Sep 17 00:00:00 2001
From: Johan Erlandsson <johan.erlandsson@xxxxxxxx>
Date: Fri, 20 Oct 2023 19:10:52 +0200
Subject: [PATCH 1/3] zram, swap cache missing page tree offset
The radix or xarray start at an offset inside struct address_space.
---
diskdump.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/diskdump.c b/diskdump.c
index 0fe46f4..f3483d8 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -2901,7 +2901,8 @@ lookup_swap_cache(ulonglong pte_val, unsigned char *zram_buf)
swp_space += (swp_offset >> SWAP_ADDRESS_SPACE_SHIFT) * SIZE(address_space);
lp.index = swp_offset;
- if ((is_xarray ? do_xarray : do_radix_tree)(swp_space, RADIX_TREE_SEARCH, &lp)) {
+ if ((is_xarray ? do_xarray : do_radix_tree)
+ (swp_space+OFFSET(address_space_page_tree), RADIX_TREE_SEARCH, &lp)) {
readmem((ulong)lp.value, KVADDR, &page, sizeof(void *),
"swap_cache page", FAULT_ON_ERROR);
if (!is_page_ptr(page, &paddr)) {
--
2.42.0
From b828f5f653145129b0f2974704aa03d32c67c1c7 Mon Sep 17 00:00:00 2001
From: Johan Erlandsson <johan.erlandsson@xxxxxxxx>
Date: Thu, 9 Nov 2023 16:13:29 +0100
Subject: [PATCH 2/3] zram, swap cache entries are pointer to struct page
The entries in radix, xarray (swap cache) are address to struct page.
---
diskdump.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/diskdump.c b/diskdump.c
index f3483d8..6bd8271 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -2903,9 +2903,7 @@ lookup_swap_cache(ulonglong pte_val, unsigned char *zram_buf)
lp.index = swp_offset;
if ((is_xarray ? do_xarray : do_radix_tree)
(swp_space+OFFSET(address_space_page_tree), RADIX_TREE_SEARCH, &lp)) {
- readmem((ulong)lp.value, KVADDR, &page, sizeof(void *),
- "swap_cache page", FAULT_ON_ERROR);
- if (!is_page_ptr(page, &paddr)) {
+ if (!is_page_ptr((ulong)lp.value, &paddr)) {
error(WARNING, "radix page: %lx: not a page pointer\n", lp.value);
return NULL;
}
--
2.42.0
From 8d04ea2d6110fa7a7a5453d98ade525de1b89585 Mon Sep 17 00:00:00 2001
From: Johan Erlandsson <johan.erlandsson@xxxxxxxx>
Date: Mon, 23 Oct 2023 15:42:32 +0200
Subject: [PATCH 3/3] zram, exclude shadow entries from swap cache lookup
radix or xarray can contain shadow entries from previous page
entries. These should be ignored when looking for a page pointer.
---
diskdump.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/diskdump.c b/diskdump.c
index 6bd8271..590762d 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -2871,6 +2871,17 @@ out:
return zram_buf;
}
+static inline bool radix_tree_exceptional_entry(ulong entry)
+{
+ return entry & RADIX_TREE_EXCEPTIONAL_ENTRY;
+}
+
+/* this already exists in maple_tree.h add to defs.h ? */
+static inline bool xa_is_value(ulong entry)
+{
+ return entry & 1;
+}
+
static unsigned char *
lookup_swap_cache(ulonglong pte_val, unsigned char *zram_buf)
{
@@ -2903,6 +2914,10 @@ lookup_swap_cache(ulonglong pte_val, unsigned char *zram_buf)
lp.index = swp_offset;
if ((is_xarray ? do_xarray : do_radix_tree)
(swp_space+OFFSET(address_space_page_tree), RADIX_TREE_SEARCH, &lp)) {
+ if ((is_xarray ? xa_is_value : radix_tree_exceptional_entry)((ulong)lp.value)) {
+ /* ignore shadow values */
+ return NULL;
+ }
if (!is_page_ptr((ulong)lp.value, &paddr)) {
error(WARNING, "radix page: %lx: not a page pointer\n", lp.value);
return NULL;
--
2.42.0
--
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