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mm/mmu_gather: define ENCODED_PAGE_FLAG_DELAY_RMAP

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Nowadays, encoded pages are only used in mmu_gather handling.  Let's
update the documentation, and define ENCODED_PAGE_BIT_DELAY_RMAP.  While
at it, rename ENCODE_PAGE_BITS to ENCODED_PAGE_BITS.

If encoded page pointers would ever be used in other context again, we'd
likely want to change the defines to reflect their context (e.g.,
ENCODED_PAGE_FLAG_MMU_GATHER_DELAY_RMAP).  For now, let's keep it simple.

This is a preparation for using the remaining spare bit to indicate that
the next item in an array of encoded pages is a "nr_pages" argument and
not an encoded page.

Link: https://lkml.kernel.org/r/20240214204435.167852-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2024-02-14 21:44:31 +01:00 committed by Andrew Morton
parent c30d6bc8d0
commit da510964c0
2 changed files with 14 additions and 8 deletions
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17
include/linux/mm_types.h
View File

@ -210,8 +210,8 @@ struct page {
*
* An 'encoded_page' pointer is a pointer to a regular 'struct page', but
* with the low bits of the pointer indicating extra context-dependent
* information. Not super-common, but happens in mmu_gather and mlock
* handling, and this acts as a type system check on that use.
* information. Only used in mmu_gather handling, and this acts as a type
* system check on that use.
*
* We only really have two guaranteed bits in general, although you could
* play with 'struct page' alignment (see CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
@ -220,21 +220,26 @@ struct page {
* Use the supplied helper functions to endcode/decode the pointer and bits.
*/
struct encoded_page;
#define ENCODE_PAGE_BITS 3ul
#define ENCODED_PAGE_BITS 3ul
/* Perform rmap removal after we have flushed the TLB. */
#define ENCODED_PAGE_BIT_DELAY_RMAP 1ul
static __always_inline struct encoded_page *encode_page(struct page *page, unsigned long flags)
{
BUILD_BUG_ON(flags > ENCODE_PAGE_BITS);
BUILD_BUG_ON(flags > ENCODED_PAGE_BITS);
return (struct encoded_page *)(flags | (unsigned long)page);
}
static inline unsigned long encoded_page_flags(struct encoded_page *page)
{
return ENCODE_PAGE_BITS & (unsigned long)page;
return ENCODED_PAGE_BITS & (unsigned long)page;
}
static inline struct page *encoded_page_ptr(struct encoded_page *page)
{
return (struct page *)(~ENCODE_PAGE_BITS & (unsigned long)page);
return (struct page *)(~ENCODED_PAGE_BITS & (unsigned long)page);
}
/*

5
mm/mmu_gather.c
View File

@ -53,7 +53,7 @@ static void tlb_flush_rmap_batch(struct mmu_gather_batch *batch, struct vm_area_
for (int i = 0; i < batch->nr; i++) {
struct encoded_page *enc = batch->encoded_pages[i];
if (encoded_page_flags(enc)) {
if (encoded_page_flags(enc) & ENCODED_PAGE_BIT_DELAY_RMAP) {
struct page *page = encoded_page_ptr(enc);
folio_remove_rmap_pte(page_folio(page), page, vma);
}
@ -119,6 +119,7 @@ static void tlb_batch_list_free(struct mmu_gather *tlb)
bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
bool delay_rmap, int page_size)
{
int flags = delay_rmap ? ENCODED_PAGE_BIT_DELAY_RMAP : 0;
struct mmu_gather_batch *batch;
VM_BUG_ON(!tlb->end);
@ -132,7 +133,7 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
* Add the page and check if we are full. If so
* force a flush.
*/
batch->encoded_pages[batch->nr++] = encode_page(page, delay_rmap);
batch->encoded_pages[batch->nr++] = encode_page(page, flags);
if (batch->nr == batch->max) {
if (!tlb_next_batch(tlb))
return true;