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Message-ID: <20240306104147.193052-14-peterx@redhat.com>
Date: Wed, 6 Mar 2024 18:41:47 +0800
From: peterx@...hat.com
To: linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org,
Andrew Morton <akpm@...ux-foundation.org>,
Muchun Song <muchun.song@...ux.dev>,
Jason Gunthorpe <jgg@...dia.com>,
peterx@...hat.com,
Matthew Wilcox <willy@...radead.org>,
Mike Rapoport <rppt@...nel.org>,
Christophe Leroy <christophe.leroy@...roup.eu>,
x86@...nel.org,
sparclinux@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: [PATCH RFC 13/13] mm: Document pXd_leaf() API
From: Peter Xu <peterx@...hat.com>
There's one small section already, but since we're going to remove
pXd_huge(), that comment may start to obsolete.
Rewrite that section with more information, hopefully with that the API is
crystal clear on what it implies.
Signed-off-by: Peter Xu <peterx@...hat.com>
---
include/linux/pgtable.h | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 85fc7554cd52..6b0d222a7fad 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1770,11 +1770,25 @@ typedef unsigned int pgtbl_mod_mask;
#endif
/*
- * p?d_leaf() - true if this entry is a final mapping to a physical address.
- * This differs from p?d_huge() by the fact that they are always available (if
- * the architecture supports large pages at the appropriate level) even
- * if CONFIG_HUGETLB_PAGE is not defined.
- * Only meaningful when called on a valid entry.
+ * pXd_leaf() is the API to check whether a pgtable entry is a huge page
+ * mapping. It should work globally across all archs, without any
+ * dependency on CONFIG_* options. For architectures that do not support
+ * huge mappings on specific levels, below fallbacks will be used.
+ *
+ * A leaf pgtable entry should always imply the following:
+ *
+ * - It is a "present" entry. IOW, before using this API, please check it
+ * with pXd_present() first. NOTE: it may not always mean the "present
+ * bit" is set. For example, PROT_NONE entries are always "present".
+ *
+ * - It should _never_ be a swap entry of any type. Above "present" check
+ * should have guarded this, but let's be crystal clear on this.
+ *
+ * - It should contain a huge PFN, which points to a huge page larger than
+ * PAGE_SIZE of the platform. The PFN format isn't important here.
+ *
+ * - It should cover all kinds of huge mappings (e.g., pXd_trans_huge(),
+ * pXd_devmap(), or hugetlb mappings).
*/
#ifndef pgd_leaf
#define pgd_leaf(x) false
--
2.44.0
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