[PATCH 3/4] libpager: Track which pages are precious

[Sergey Bugaev]

This introduces the PM_PRECIOUS bit, which gets set when a precious
page is offered to the kernel using pager_offer_page () with the
precious argument set, and cleared when the page is returned back.
---
 libpager/data-return.c | 3 ++-
 libpager/offer-page.c  | 2 ++
 libpager/priv.h        | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/libpager/data-return.c b/libpager/data-return.c
index db2f84e6..2cc9f1f8 100644
--- a/libpager/data-return.c
+++ b/libpager/data-return.c
@@ -214,7 +214,8 @@ _pager_do_write_request (struct pager *p,
            pm_entries[i] &= ~PM_INCORE;
        }
 
-      pm_entries[i] &= ~(PM_PAGINGOUT | PM_PAGEINWAIT | PM_WRITEWAIT);
+      pm_entries[i] &= ~(PM_PAGINGOUT | PM_PAGEINWAIT
+                       | PM_WRITEWAIT | PM_PRECIOUS);
     }
 
   for (ll = lock_list; ll; ll = ll->next)
diff --git a/libpager/offer-page.c b/libpager/offer-page.c
index 26f88ca3..392e83b8 100644
--- a/libpager/offer-page.c
+++ b/libpager/offer-page.c
@@ -38,6 +38,8 @@ pager_offer_page (struct pager *p,
 
   short *pm_entry = &p->pagemap[offset / vm_page_size];
   *pm_entry |= PM_INCORE;
+  if (precious)
+    *pm_entry |= PM_PRECIOUS;
 
   err = memory_object_data_supply (p->memobjcntl, offset, buf, vm_page_size, 0,
                                    writelock ? VM_PROT_WRITE : VM_PROT_NONE,
diff --git a/libpager/priv.h b/libpager/priv.h
index d9d76965..a5e22f36 100644
--- a/libpager/priv.h
+++ b/libpager/priv.h
@@ -108,6 +108,7 @@ extern int _pager_page_errors[];
 
 /* Pagemap format */
 /* These are binary state bits */
+#define PM_PRECIOUS   0x0400   /* return even if not dirty */
 #define PM_WRITEWAIT  0x0200   /* queue wakeup once write is done */
 #define PM_INIT       0x0100    /* data has been written */
 #define PM_INCORE     0x0080   /* kernel might have a copy */
-- 
2.31.1