On Thu, 2007-12-20 at 15:26 +0000, Hugh Dickins wrote:
> The asynch code: perhaps not worth doing for MADV_WILLNEED alone,
> but might prove useful for more general use when swapping in.
> Not really the same as Con's swap prefetch, but worth looking
> at that for reference. But I guess this becomes a much bigger
> issue than you were intending to get into here.
heh, yeah, got somewhat more complex that I'd hoped for.
last patch for today (not even compile tested), will do a proper patch
and test it tomorrow.
---
A best effort MADV_WILLNEED implementation for anonymous memory.
It adds a batch method to the page table walk routines so we can
copy a few ptes while holding the kmap, which makes it possible to
allocate the backing pages using GFP_KERNEL.
Signed-off-by: Peter Zijlstra <[email protected]>
---
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5c3655f..391a453 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -726,6 +726,7 @@ unsigned long unmap_vmas(struct mmu_gather **tlb,
* @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry
* @pte_entry: if set, called for each non-empty PTE (4th-level) entry
* @pte_hole: if set, called for each hole at all levels
+ * @pte_batch: if set, called for each %WALK_BATCH_SIZE PTE entries.
*
* (see walk_page_range for more details)
*/
@@ -735,8 +736,16 @@ struct mm_walk {
int (*pmd_entry)(pmd_t *, unsigned long, unsigned long, void *);
int (*pte_entry)(pte_t *, unsigned long, unsigned long, void *);
int (*pte_hole)(unsigned long, unsigned long, void *);
+ int (*pte_batch)(unsigned long, unsigned long, void *);
};
+#define WALK_BATCH_SIZE 32
+
+static inline walk_addr_index(unsigned long addr)
+{
+ return (addr >> PAGE_SHIFT) % WALK_BATCH_SIZE;
+}
+
int walk_page_range(const struct mm_struct *, unsigned long addr,
unsigned long end, const struct mm_walk *walk,
void *private);
diff --git a/mm/madvise.c b/mm/madvise.c
index 93ee375..86610a0 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -11,6 +11,8 @@
#include <linux/mempolicy.h>
#include <linux/hugetlb.h>
#include <linux/sched.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
/*
* Any behaviour which results in changes to the vma->vm_flags needs to
@@ -100,17 +102,71 @@ out:
return error;
}
+struct madvise_willneed_anon_data {
+ pte_t entries[WALK_BATCH_SIZE];
+ struct vm_area_struct *vma;
+}
+
+static int madvise_willneed_anon_pte(pte_t *ptep,
+ unsigned long addr, unsigned long end, void *arg)
+{
+ struct madvise_willneed_anon_data *data = arg;
+
+ data->entries[walk_addr_index(addr)] = *ptep;
+
+ return 0;
+}
+
+static int madvise_willneed_anon_batch(unsigned long addr,
+ unsigned long end, void *arg)
+{
+ struct madvise_willneed_anon_data *data = arg;
+ unsigned int i;
+
+ for (; addr != end; addr += PAGE_SIZE) {
+ pte_t pte = data->entries[walk_addr_index(addr)];
+
+ if (is_swap_pte(pte)) {
+ struct page *page =
+ read_swap_cache_async(pte_to_swp_entry(pte),
+ GFP_KERNEL, data->vma, addr);
+ if (page)
+ page_cache_release(page);
+ }
+ }
+
+ return 0;
+}
+
+static long madvise_willneed_anon(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ struct madvise_willneed_anon_data data = {
+ .vma = vma;
+ };
+ struct mm_walk walk = {
+ .pte_entry = madvise_willneed_anon_pte,
+ .pte_batch = madvise_willneed_anon_batch,
+ };
+
+ *prev = vma;
+ walk_page_range(vma->vm_mm, start, end, &walk, vma);
+
+ return 0;
+}
+
/*
* Schedule all required I/O operations. Do not wait for completion.
*/
-static long madvise_willneed(struct vm_area_struct * vma,
- struct vm_area_struct ** prev,
+static long madvise_willneed(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
unsigned long start, unsigned long end)
{
struct file *file = vma->vm_file;
if (!file)
- return -EBADF;
+ return madvise_willneed_anon(vma, prev, start, end);
if (file->f_mapping->a_ops->get_xip_page) {
/* no bad return value, but ignore advice */
@@ -119,8 +175,6 @@ static long madvise_willneed(struct vm_area_struct * vma,
*prev = vma;
start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
- if (end > vma->vm_end)
- end = vma->vm_end;
end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
force_page_cache_readahead(file->f_mapping,
@@ -147,8 +201,8 @@ static long madvise_willneed(struct vm_area_struct * vma,
* An interface that causes the system to free clean pages and flush
* dirty pages is already available as msync(MS_INVALIDATE).
*/
-static long madvise_dontneed(struct vm_area_struct * vma,
- struct vm_area_struct ** prev,
+static long madvise_dontneed(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
unsigned long start, unsigned long end)
{
*prev = vma;
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index b4f27d2..25fc656 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -2,12 +2,45 @@
#include <linux/highmem.h>
#include <linux/sched.h>
+static int walk_pte_range_batch(pmd_t *pmd, unsigned long addr, unsigned long end,
+ const struct mm_walk *walk, void *private)
+{
+ int err = 0;
+
+ do {
+ unsigned int i;
+ pte_t *pte;
+ unsigned long start = addr;
+ int err2;
+
+ pte = pte_offset_map(pmd, addr);
+ for (i = 0; i < WALK_BATCH_SIZE && addr != end;
+ i++, pte++, addr += PAGE_SIZE) {
+ err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, private);
+ if (err)
+ break;
+ }
+ pte_unmap(pte);
+
+ err2 = walk->pte_batch(start, end, private);
+ if (!err)
+ err = err2;
+ if (err)
+ break;
+ } while (addr != end);
+
+ return err;
+}
+
static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
const struct mm_walk *walk, void *private)
{
pte_t *pte;
int err = 0;
+ if (walk->pte_batch)
+ return walk_pte_range_batch(pmd, addr, end, walk, private);
+
pte = pte_offset_map(pmd, addr);
do {
err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, private);
--
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