Re: [PATCH v2] mm/hugetlb: mm/memory_hotplug: use a folio in scan_movable_pages()

From: Sidhartha Kumar
Date: Fri May 31 2024 - 13:39:38 EST


On 5/31/24 6:05 AM, David Hildenbrand wrote:
On 31.05.24 15:04, David Hildenbrand wrote:
On 30.05.24 19:14, Sidhartha Kumar wrote:
By using a folio in scan_movable_pages() we convert the last user of the
page-based hugetlb information macro functions to the folio version.
After this conversion, we can safely remove the page-based definitions
from include/linux/hugetlb.h.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
---

v1 -> v2:
    simplify pfn skipping logic with pfn |= folio_nr_pages(folio) - 1
    per Matthew

   include/linux/hugetlb.h |  6 +-----
   mm/memory_hotplug.c     | 11 +++++------
   2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 15a58f69782c..279aca379b95 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -616,9 +616,7 @@ static __always_inline                        \
   bool folio_test_hugetlb_##flname(struct folio *folio)        \
       {    void *private = &folio->private;        \
           return test_bit(HPG_##flname, private);        \
-    }                            \
-static inline int HPage##uname(struct page *page)        \
-    { return test_bit(HPG_##flname, &(page->private)); }
+    }
   #define SETHPAGEFLAG(uname, flname)                \
   static __always_inline                        \
@@ -637,8 +635,6 @@ void folio_clear_hugetlb_##flname(struct folio *folio)        \
   #define TESTHPAGEFLAG(uname, flname)                \
   static inline bool                        \
   folio_test_hugetlb_##flname(struct folio *folio)        \
-    { return 0; }                        \
-static inline int HPage##uname(struct page *page)        \
       { return 0; }
   #define SETHPAGEFLAG(uname, flname)                \
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 431b1f6753c0..9c36eb3bbd3b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1731,8 +1731,8 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
       unsigned long pfn;
       for (pfn = start; pfn < end; pfn++) {
-        struct page *page, *head;
-        unsigned long skip;
+        struct page *page;
+        struct folio *folio;
           if (!pfn_valid(pfn))
               continue;
@@ -1753,7 +1753,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
           if (!PageHuge(page))
               continue;
-        head = compound_head(page);
+        folio = page_folio(page);
           /*
            * This test is racy as we hold no reference or lock.  The
            * hugetlb page could have been free'ed and head is no longer
@@ -1761,10 +1761,9 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
            * cases false positives and negatives are possible.  Calling
            * code must deal with these scenarios.
            */
-        if (HPageMigratable(head))
+        if (folio_test_hugetlb_migratable(folio))
               goto found;
-        skip = compound_nr(head) - (pfn - page_to_pfn(head));
-        pfn += skip - 1;
+        pfn |= folio_nr_pages(folio) - 1;

Likely not exactly what we want?

pfn |= folio_nr_pages(folio);

Would make sure that we are "one PFN before the start of the next
folio". The pfn++ before the next loop iteration would move us to the
next folio.

Or am I missing something?

Okay, I got it wrong.

"folio_nr_pages(folio) - 1" gives us the bitmask to land one PFN before the end.

ya because folio_nr_pages() will be a power of 2, subtracting 1 turns it into a bitmask.


Acked-by: David Hildenbrand <david@xxxxxxxxxx>


Thanks for taking a look at this.


It might be cleaner if we would handle the "pfn++;" on the "continue;"
paths inmstead, and simply here do something like

    pfn = ALIGN(pfn + 1, folio_nr_pages(folio));

instead.