mm/mmu_gather: add __tlb_remove_folio_pages()

Add __tlb_remove_folio_pages(), which will remove multiple consecutive
pages that belong to the same large folio, instead of only a single page. 
We'll be using this function when optimizing unmapping/zapping of large
folios that are mapped by PTEs.

We're using the remaining spare bit in an encoded_page to indicate that
the next enoced page in an array contains actually shifted "nr_pages". 
Teach swap/freeing code about putting multiple folio references, and
delayed rmap handling to remove page ranges of a folio.

This extension allows for still gathering almost as many small folios as
we used to (-1, because we have to prepare for a possibly bigger next
entry), but still allows for gathering consecutive pages that belong to
the same large folio.

Note that we don't pass the folio pointer, because it is not required for
now.  Further, we don't support page_size != PAGE_SIZE, it won't be
required for simple PTE batching.

We have to provide a separate s390 implementation, but it's fairly
straight forward.

Another, more invasive and likely more expensive, approach would be to use
folio+range or a PFN range instead of page+nr_pages.  But, we should do
that consistently for the whole mmu_gather.  For now, let's keep it simple
and add "nr_pages" only.

Note that it is now possible to gather significantly more pages: In the
past, we were able to gather ~10000 pages, now we can also gather ~5000
folio fragments that span multiple pages.  A folio fragment on x86-64 can
span up to 512 pages (2 MiB THP) and on arm64 with 64k in theory 8192
pages (512 MiB THP).  Gathering more memory is not considered something we
should worry about, especially because these are already corner cases.

While we can gather more total memory, we won't free more folio fragments.
As long as page freeing time primarily only depends on the number of
involved folios, there is no effective change for !preempt configurations.
However, we'll adjust tlb_batch_pages_flush() separately to handle corner
cases where page freeing time grows proportionally with the actual memory
size.

Link: https://lkml.kernel.org/r/20240214204435.167852-9-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>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 127a8230a40a..709830274b75 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -69,6 +69,7 @@
  *
  *  - tlb_remove_page() / __tlb_remove_page()
  *  - tlb_remove_page_size() / __tlb_remove_page_size()
+ *  - __tlb_remove_folio_pages()
  *
  *    __tlb_remove_page_size() is the basic primitive that queues a page for
  *    freeing. __tlb_remove_page() assumes PAGE_SIZE. Both will return a
@@ -78,6 +79,11 @@
  *    tlb_remove_page() and tlb_remove_page_size() imply the call to
  *    tlb_flush_mmu() when required and has no return value.
  *
+ *    __tlb_remove_folio_pages() is similar to __tlb_remove_page(), however,
+ *    instead of removing a single page, remove the given number of consecutive
+ *    pages that are all part of the same (large) folio: just like calling
+ *    __tlb_remove_page() on each page individually.
+ *
  *  - tlb_change_page_size()
  *
  *    call before __tlb_remove_page*() to set the current page-size; implies a
@@ -262,6 +268,8 @@ struct mmu_gather_batch {
 
 extern bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
 		bool delay_rmap, int page_size);
+bool __tlb_remove_folio_pages(struct mmu_gather *tlb, struct page *page,
+		unsigned int nr_pages, bool delay_rmap);
 
 #ifdef CONFIG_SMP
 /*