On 25.04.24 10:50, Lance Yang wrote:
Hey Zi, David,
Hi,
How about this change(diff against mm-unstable) as follows?
goes into the right direction, please resent the whole thing, that will
make it easier to review.
I'd like to add __try_to_unmap_huge_pmd() as a new internal function
specifically for unmapping PMD-mapped folios. If, for any reason, we cannot
unmap the folio, then we'll still split it as previously done.
Currently, __try_to_unmap_huge_pmd() only handles lazyfree THPs, but it
can be extended to support other large folios that are PMD-mapped in the
future if needed.
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 670218f762c8..0f906dc6d280 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -100,8 +100,6 @@ enum ttu_flags {
* do a final flush if necessary */
TTU_RMAP_LOCKED = 0x80, /* do not grab rmap lock:
* caller holds it */
- TTU_LAZYFREE_THP = 0x100, /* avoid splitting PMD-mapped THPs
- * that are marked as lazyfree. */
};
#ifdef CONFIG_MMU
diff --git a/mm/rmap.c b/mm/rmap.c
index a7913a454028..879c8923abfc 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1606,6 +1606,19 @@ void folio_remove_rmap_pmd(struct folio *folio, struct page *page,
#endif
}
+static bool __try_to_unmap_huge_pmd(struct vm_area_struct *vma,
+ unsigned long addr, struct folio *folio)
+{
+ VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio);
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ if (folio_test_anon(folio) && !folio_test_swapbacked(folio))
+ return discard_trans_pmd(vma, addr, folio);
+#endif
+
+ return false;
+}
+
/*
* @arg: enum ttu_flags will be passed to this argument
*/
@@ -1631,14 +1644,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
if (flags & TTU_SYNC)
pvmw.flags = PVMW_SYNC;
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- if (flags & TTU_LAZYFREE_THP)
- if (discard_trans_pmd(vma, address, folio))
+ if (flags & TTU_SPLIT_HUGE_PMD) {
+ if (__try_to_unmap_huge_pmd(vma, address, folio))
return true;
-#endif
-
- if (flags & TTU_SPLIT_HUGE_PMD)
split_huge_pmd_address(vma, address, false, folio);
+ }
I was wondering if we can better integrate that into the pagewalk below.
That is, don't do the TTU_SPLIT_HUGE_PMD immediately. Start the pagewalk
first. If we walk a PMD, try to unmap it. Only if that fails, split it.
Less working on "vma + address" and instead directly on PMDs.
--
Cheers,
David / dhildenb
