On Mon, Feb 11, 2013 at 02:12:39PM -0800, Andrew Morton wrote:
> Also, having to mmap the file to be able to query pagecache state is a
> hack. Whatever happened to the fincore() patch?
I don't know, but how about this one:
---
From: Johannes Weiner <han...@cmpxchg.org>
Subject: [patch 1/2] mm: fincore()
Provide a syscall to determine whether a given file's pages are cached
in memory. This is more elegant than mmapping the file for the sole
purpose of using mincore(), and also works on NOMMU.
Signed-off-by: Johannes Weiner <han...@cmpxchg.org>
---
include/linux/syscalls.h | 2 +
mm/Makefile | 2 +-
mm/fincore.c | 128 +++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 131 insertions(+), 1 deletion(-)
create mode 100644 mm/fincore.c
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 313a8e0..3ceab2a 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -897,4 +897,6 @@ asmlinkage long sys_process_vm_writev(pid_t pid,
asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
unsigned long idx1, unsigned long idx2);
asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags);
+asmlinkage long sys_fincore(unsigned int fd, loff_t start, loff_t len,
+ unsigned char __user * vec);
#endif
diff --git a/mm/Makefile b/mm/Makefile
index 185a22b..221cdae 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -17,7 +17,7 @@ obj-y := filemap.o mempool.o oom_kill.o
fadvise.o \
util.o mmzone.o vmstat.o backing-dev.o \
mm_init.o mmu_context.o percpu.o slab_common.o \
compaction.o balloon_compaction.o \
- interval_tree.o $(mmu-y)
+ interval_tree.o fincore.o $(mmu-y)
obj-y += init-mm.o
diff --git a/mm/fincore.c b/mm/fincore.c
new file mode 100644
index 0000000..d504611
--- /dev/null
+++ b/mm/fincore.c
@@ -0,0 +1,128 @@
+#include <linux/syscalls.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+
+static long do_fincore(struct address_space *mapping, pgoff_t pgstart,
+ unsigned long nr_pages, unsigned char *vec)
+{
+ pgoff_t pgend = pgstart + nr_pages;
+ struct radix_tree_iter iter;
+ void **slot;
+ long nr = 0;
+
+ rcu_read_lock();
+restart:
+ radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, pgstart) {
+ unsigned char present;
+ struct page *page;
+
+ /* Handle holes */
+ if (iter.index != pgstart + nr) {
+ if (iter.index < pgend)
+ nr_pages = iter.index - pgstart;
+ break;
+ }
+repeat:
+ page = radix_tree_deref_slot(slot);
+ if (unlikely(!page))
+ continue;
+
+ if (radix_tree_exception(page)) {
+ if (radix_tree_deref_retry(page)) {
+ /*
+ * Transient condition which can only trigger
+ * when entry at index 0 moves out of or back
+ * to root: none yet gotten, safe to restart.
+ */
+ WARN_ON(iter.index);
+ goto restart;
+ }
+ present = 0;
+ } else {
+ if (!page_cache_get_speculative(page))
+ goto repeat;
+
+ /* Has the page moved? */
+ if (unlikely(page != *slot)) {
+ page_cache_release(page);
+ goto repeat;
+ }
+
+ present = PageUptodate(page);
+ page_cache_release(page);
+ }
+ vec[nr] = present;
+
+ if (++nr == nr_pages)
+ break;
+ }
+ rcu_read_unlock();
+
+ if (nr < nr_pages)
+ memset(vec + nr, 0, nr_pages - nr);
+
+ return nr_pages;
+}
+
+/*
+ * The fincore(2) system call.
+ *
+ * fincore() returns the memory residency status of the given file's
+ * pages, in the range [start, start + len].
+ * The status is returned in a vector of bytes. The least significant
+ * bit of each byte is 1 if the referenced page is in memory, otherwise
+ * it is zero.
+ *
+ * Because the status of a page can change after fincore() checks it
+ * but before it returns to the application, the returned vector may
+ * contain stale information.
+ *
+ * return values:
+ * zero - success
+ * -EBADF - fd isn't a valid open file descriptor
+ * -EFAULT - vec points to an illegal address
+ * -EINVAL - start is not a multiple of PAGE_CACHE_SIZE
+ */
+SYSCALL_DEFINE4(fincore, unsigned int, fd, loff_t, start, loff_t, len,
+ unsigned char __user *, vec)
+{
+ unsigned long nr_pages;
+ pgoff_t pgstart;
+ struct fd f;
+ long ret;
+
+ if (start & ~PAGE_CACHE_MASK)
+ return -EINVAL;
+
+ f = fdget(fd);
+ if (!f.file)
+ return -EBADF;
+
+ pgstart = start >> PAGE_CACHE_SHIFT;
+ nr_pages = DIV_ROUND_UP(len, PAGE_CACHE_SIZE);
+
+ while (nr_pages) {
+ unsigned char tmp[64];
+
+ ret = do_fincore(f.file->f_mapping, pgstart,
+ min(nr_pages, sizeof(tmp)), tmp);
+ if (ret <= 0)
+ break;
+
+ if (copy_to_user(vec, tmp, ret)) {
+ ret = -EFAULT;
+ break;
+ }
+
+ nr_pages -= ret;
+ pgstart += ret;
+ vec += ret;
+ ret = 0;
+ }
+
+ fdput(f);
+
+ return ret;
+}
--
1.7.11.7
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