On 01.09.21 22:57, Peter Xu wrote:
Instead of trying to introduce one variable for every new zap_details fields,
let's introduce a flag so that it can start to encode true/false informations.
Let's start to use this flag first to clean up the only check_mapping variable.
Firstly, the name "check_mapping" implies this is a "boolean", but actually it
stores the mapping inside, just in a way that it won't be set if we don't want
to check the mapping.
To make things clearer, introduce the 1st zap flag ZAP_FLAG_CHECK_MAPPING, so
that we only check against the mapping if this bit set. At the same time, we
can rename check_mapping into zap_mapping and set it always.
Since at it, introduce another helper zap_check_mapping_skip() and use it in
zap_pte_range() properly.
Some old comments have been removed in zap_pte_range() because they're
duplicated, and since now we're with ZAP_FLAG_CHECK_MAPPING flag, it'll be very
easy to grep this information by simply grepping the flag.
It'll also make life easier when we want to e.g. pass in zap_flags into the
callers like unmap_mapping_pages() (instead of adding new booleans besides the
even_cows parameter).
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
include/linux/mm.h | 19 ++++++++++++++++++-
mm/memory.c | 34 ++++++++++------------------------
2 files changed, 28 insertions(+), 25 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 69259229f090..fcbc1c4f8e8e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1716,14 +1716,31 @@ static inline bool can_do_mlock(void) { return false; }
extern int user_shm_lock(size_t, struct ucounts *);
extern void user_shm_unlock(size_t, struct ucounts *);
+/* Whether to check page->mapping when zapping */
+#define ZAP_FLAG_CHECK_MAPPING BIT(0)
So we want to go full way, like:
typedef int __bitwise zap_flags_t;
#define ZAP_FLAG_CHECK_MAPPING ((__force zap_flags_t)BIT(0))
+
/*
* Parameter block passed down to zap_pte_range in exceptional cases.
*/
struct zap_details {
- struct address_space *check_mapping; /* Check page->mapping if set */
+ struct address_space *zap_mapping;
struct page *single_page; /* Locked page to be unmapped */
+ unsigned long zap_flags;
Why call it "zap_*" if everything in the structure is related to
zapping? IOW, simply "mapping", "flags" would be good enough.
};
+/* Return true if skip zapping this page, false otherwise */
+static inline bool
+zap_skip_check_mapping(struct zap_details *details, struct page *page)
+{
+ if (!details || !page)
+ return false;
+
+ if (!(details->zap_flags & ZAP_FLAG_CHECK_MAPPING))
+ return false;
+
+ return details->zap_mapping != page_rmapping(page);
+}
I'm confused, why isn't "!details->zap_mapping" vs.
"details->zap_mapping" sufficient? I can see that you may need flags for
other purposes (next patch), but why do we need it here?
Factoring it out into this helper is a nice cleanup, though. But I'd
just not introduce ZAP_FLAG_CHECK_MAPPING.
--
Thanks,
David / dhildenb
