[SPARC64]: Dynamically grow TSB in response to RSS growth.

As the RSS grows, grow the TSB in order to reduce the likelyhood
of hash collisions and thus poor hit rates in the TSB.

This definitely needs some serious tuning.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 145 insertions, 6 deletions

diff --git a/arch/sparc64/mm/tsb.c b/arch/sparc64/mm/tsb.c
index dfe7144fcdf6..707af4b84a0e 100644
--- a/arch/sparc64/mm/tsb.c
+++ b/arch/sparc64/mm/tsb.c
@@ -10,6 +10,7 @@
 #include <asm/tlb.h>
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
+#include <asm/tsb.h>
 
 /* We use an 8K TSB for the whole kernel, this allows to
  * handle about 4MB of modules and vmalloc mappings without
@@ -146,6 +147,9 @@ static void setup_tsb_params(struct mm_struct *mm, unsigned long tsb_bytes)
                 tte |= _PAGE_SZ4MB;
                 page_sz = 4 * 1024 * 1024;
                 break;
+
+        default:
+                BUG();
         };
 
         tsb_reg |= base;
@@ -157,23 +161,158 @@ static void setup_tsb_params(struct mm_struct *mm, unsigned long tsb_bytes)
         mm->context.tsb_map_pte = tte;
 }
 
+/* The page tables are locked against modifications while this
+ * runs.
+ *
+ * XXX do some prefetching...
+ */
+static void copy_tsb(struct tsb *old_tsb, unsigned long old_size,
+                     struct tsb *new_tsb, unsigned long new_size)
+{
+        unsigned long old_nentries = old_size / sizeof(struct tsb);
+        unsigned long new_nentries = new_size / sizeof(struct tsb);
+        unsigned long i;
+
+        for (i = 0; i < old_nentries; i++) {
+                register unsigned long tag asm("o4");
+                register unsigned long pte asm("o5");
+                unsigned long v;
+                unsigned int hash;
+
+                __asm__ __volatile__(
+                        "ldda [%2] %3, %0"
+                        : "=r" (tag), "=r" (pte)
+                        : "r" (&old_tsb[i]), "i" (ASI_NUCLEUS_QUAD_LDD));
+
+                if (!tag || (tag & TSB_TAG_LOCK))
+                        continue;
+
+                /* We only put base page size PTEs into the TSB,
+                 * but that might change in the future.  This code
+                 * would need to be changed if we start putting larger
+                 * page size PTEs into there.
+                 */
+                WARN_ON((pte & _PAGE_ALL_SZ_BITS) != _PAGE_SZBITS);
+
+                /* The tag holds bits 22 to 63 of the virtual address
+                 * and the context.  Clear out the context, and shift
+                 * up to make a virtual address.
+                 */
+                v = (tag & ((1UL << 42UL) - 1UL)) << 22UL;
+
+                /* The implied bits of the tag (bits 13 to 21) are
+                 * determined by the TSB entry index, so fill that in.
+                 */
+                v |= (i & (512UL - 1UL)) << 13UL;
+
+                hash = tsb_hash(v, new_nentries);
+                new_tsb[hash].tag = tag;
+                new_tsb[hash].pte = pte;
+        }
+}
+
+/* When the RSS of an address space exceeds mm->context.tsb_rss_limit,
+ * update_mmu_cache() invokes this routine to try and grow the TSB.
+ * When we reach the maximum TSB size supported, we stick ~0UL into
+ * mm->context.tsb_rss_limit so the grow checks in update_mmu_cache()
+ * will not trigger any longer.
+ *
+ * The TSB can be anywhere from 8K to 1MB in size, in increasing powers
+ * of two.  The TSB must be aligned to it's size, so f.e. a 512K TSB
+ * must be 512K aligned.
+ *
+ * The idea here is to grow the TSB when the RSS of the process approaches
+ * the number of entries that the current TSB can hold at once.  Currently,
+ * we trigger when the RSS hits 3/4 of the TSB capacity.
+ */
+void tsb_grow(struct mm_struct *mm, unsigned long rss, gfp_t gfp_flags)
+{
+        unsigned long max_tsb_size = 1 * 1024 * 1024;
+        unsigned long size, old_size;
+        struct page *page;
+        struct tsb *old_tsb;
+
+        if (max_tsb_size > (PAGE_SIZE << MAX_ORDER))
+                max_tsb_size = (PAGE_SIZE << MAX_ORDER);
+
+        for (size = PAGE_SIZE; size < max_tsb_size; size <<= 1UL) {
+                unsigned long n_entries = size / sizeof(struct tsb);
+
+                n_entries = (n_entries * 3) / 4;
+                if (n_entries > rss)
+                        break;
+        }
+
+        page = alloc_pages(gfp_flags | __GFP_ZERO, get_order(size));
+        if (unlikely(!page))
+                return;
+
+        if (size == max_tsb_size)
+                mm->context.tsb_rss_limit = ~0UL;
+        else
+                mm->context.tsb_rss_limit =
+                        ((size / sizeof(struct tsb)) * 3) / 4;
+
+        old_tsb = mm->context.tsb;
+        old_size = mm->context.tsb_nentries * sizeof(struct tsb);
+
+        if (old_tsb)
+                copy_tsb(old_tsb, old_size, page_address(page), size);
+
+        mm->context.tsb = page_address(page);
+        setup_tsb_params(mm, size);
+
+        /* If old_tsb is NULL, we're being invoked for the first time
+         * from init_new_context().
+         */
+        if (old_tsb) {
+                /* Now force all other processors to reload the new
+                 * TSB state.
+                 */
+                smp_tsb_sync(mm);
+
+                /* Finally reload it on the local cpu.  No further
+                 * references will remain to the old TSB and we can
+                 * thus free it up.
+                 */
+                tsb_context_switch(mm);
+
+                free_pages((unsigned long) old_tsb, get_order(old_size));
+        }
+}
+
 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 {
-        unsigned long page = get_zeroed_page(GFP_KERNEL);
+        unsigned long initial_rss;
 
         mm->context.sparc64_ctx_val = 0UL;
-        if (unlikely(!page))
-                return -ENOMEM;
 
-        mm->context.tsb = (struct tsb *) page;
-        setup_tsb_params(mm, PAGE_SIZE);
+        /* copy_mm() copies over the parent's mm_struct before calling
+         * us, so we need to zero out the TSB pointer or else tsb_grow()
+         * will be confused and think there is an older TSB to free up.
+         */
+        mm->context.tsb = NULL;
+
+        /* If this is fork, inherit the parent's TSB size.  We would
+         * grow it to that size on the first page fault anyways.
+         */
+        initial_rss = mm->context.tsb_nentries;
+        if (initial_rss)
+                initial_rss -= 1;
+
+        tsb_grow(mm, initial_rss, GFP_KERNEL);
+
+        if (unlikely(!mm->context.tsb))
+                return -ENOMEM;
 
         return 0;
 }
 
 void destroy_context(struct mm_struct *mm)
 {
-        free_page((unsigned long) mm->context.tsb);
+        unsigned long size = mm->context.tsb_nentries * sizeof(struct tsb);
+
+        free_pages((unsigned long) mm->context.tsb, get_order(size));
 
         /* We can remove these later, but for now it's useful
          * to catch any bogus post-destroy_context() references