Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: 2024-07-11 18:08:16
Also in:
linux-crypto, linux-mm, linux-patches, lkml
Subsystem:
memory management, memory management - mglru (multi-gen lru), memory management - reclaim, memory management - rmap (reverse mapping), the rest · Maintainers:
Andrew Morton, Johannes Weiner, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds
On Thu, Jul 11, 2024 at 07:56:39PM +0200, Jason A. Donenfeld wrote:
On Thu, Jul 11, 2024 at 07:54:34PM +0200, Jason A. Donenfeld wrote:quoted
On Thu, Jul 11, 2024 at 07:27:27PM +0200, David Hildenbrand wrote:quoted
quoted
PG_owner_priv_1 maps to PG_swapcache? :)Maybe the combination !swapbacked && swapcache could be used to indicate such folios. (we will never set swapbacked) But likely we have to be a bit careful here. We don't want folio_test_swapcache() to return for folios that ... are not in the swapcache.I was thinking that too, but I'm afraid it's going to be another whack-a-mole nightmare. Even for things like task_mmu in procfs that show stats, that's going to be wonky. Any other flags we can overload that aren't going to be already used in our case?PG_error / folio_set_error seems unused in the non-IO case.
And PG_large_rmappable seems to only be used for hugetlb branches.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index b9e914e1face..7fdc03197438 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h@@ -190,6 +190,7 @@ enum pageflags { /* At least one page in this folio has the hwpoison flag set */ PG_has_hwpoisoned = PG_error, PG_large_rmappable = PG_workingset, /* anon or file-backed */ + PG_droppable = PG_error, /* anon droppable, not hugetlb */ }; #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
@@ -640,6 +641,8 @@ FOLIO_TEST_CLEAR_FLAG_FALSE(young) FOLIO_FLAG_FALSE(idle) #endif +FOLIO_FLAG(droppable, FOLIO_SECOND_PAGE) + /* * PageReported() is used to track reported free pages within the Buddy * allocator. We can use the non-atomic version of the test and set
diff --git a/mm/rmap.c b/mm/rmap.c
index 1f9b5a9cb121..73b4052b2f82 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c@@ -1403,6 +1403,8 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma, */ if (!(vma->vm_flags & VM_DROPPABLE)) __folio_set_swapbacked(folio); + else + folio_set_droppable(folio); __folio_set_anon(folio, vma, address, true); if (likely(!folio_test_large(folio))) {
@@ -1852,7 +1854,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * ones can be dropped even if they've * been dirtied. */ - (vma->vm_flags & VM_DROPPABLE))) { + folio_test_droppable(folio))) { dec_mm_counter(mm, MM_ANONPAGES); goto discard; }
@@ -1866,7 +1868,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * Unlike MADV_FREE mappings, VM_DROPPABLE ones * never get swap backed on failure to drop. */ - if (!(vma->vm_flags & VM_DROPPABLE)) + if (!folio_test_droppable(folio)) folio_set_swapbacked(folio); ret = false; page_vma_mapped_walk_done(&pvmw);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2e34de9cd0d4..41340f2a12c7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c@@ -4266,7 +4266,8 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c } /* dirty lazyfree */ - if (type == LRU_GEN_FILE && folio_test_anon(folio) && folio_test_dirty(folio)) { + if (type == LRU_GEN_FILE && folio_test_anon(folio) && + folio_test_dirty(folio) && !folio_test_droppable(folio)) { success = lru_gen_del_folio(lruvec, folio, true); VM_WARN_ON_ONCE_FOLIO(!success, folio); folio_set_swapbacked(folio);