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SubjectRe: [PATCH -v8 3/4] Enable the MS_ASYNC functionality in sys_msync()


On Wed, 23 Jan 2008, Peter Zijlstra wrote:
>
> It would need some addition piece to not call msync_interval() for
> MS_SYNC, and remove the balance_dirty_pages_ratelimited_nr() stuff.
>
> But yeah, this pte walker is much better.

Actually, I think this patch is much better.

Anyway, it's better because:
- it actually honors the range
- it uses the same code for MS_ASYNC and MS_SYNC
- it just avoids doing the "wait for" for MS_ASYNC.

However, it's totally untested, of course. What did you expect? Clean code
_and_ testing?

[ Side note: it is quite possible that we should not do the
SYNC_FILE_RANGE_WAIT_BEFORE on MS_ASYNC, and just skip over pages that
are busily under writeback already.

Whatever.

There are probably other problems here too, so consider this a "Hey,
wouldn't something like this work really well?" patch rather than
something final. ]

Just to get peoples creative juices going, here's my suggested patch.

Linus

---
mm/msync.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++----
1 files changed, 48 insertions(+), 4 deletions(-)
diff --git a/mm/msync.c b/mm/msync.c
index 144a757..a7a2ea4 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -10,10 +10,37 @@
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/mman.h>
+#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/syscalls.h>
#include <linux/sched.h>

+static int msync_range(struct file *file, loff_t start, unsigned long len, unsigned int sync)
+{
+ int ret;
+ struct address_space *mapping = file->f_mapping;
+ loff_t end = start + len - 1;
+
+ ret = do_sync_mapping_range(mapping, start, end,
+ SYNC_FILE_RANGE_WRITE | SYNC_FILE_RANGE_WAIT_BEFORE);
+
+ if (ret || !sync)
+ return ret;
+
+ if (file->f_op && file->f_op->fsync) {
+ mutex_lock(&mapping->host->i_mutex);
+ ret = file->f_op->fsync(file, file->f_path.dentry, 0);
+ mutex_unlock(&mapping->host->i_mutex);
+
+ if (ret < 0)
+ return ret;
+ }
+
+ return wait_on_page_writeback_range(mapping,
+ start >> PAGE_CACHE_SHIFT,
+ end >> PAGE_CACHE_SHIFT);
+}
+
/*
* MS_SYNC syncs the entire file - including mappings.
*
@@ -77,18 +104,35 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
goto out_unlock;
}
file = vma->vm_file;
- start = vma->vm_end;
- if ((flags & MS_SYNC) && file &&
- (vma->vm_flags & VM_SHARED)) {
+
+ if (file && (vma->vm_flags & VM_SHARED)) {
+ loff_t offset;
+ unsigned long len;
+
+ /*
+ * We need to do all of this before we release the mmap_sem,
+ * since "vma" isn't available after that.
+ */
+ offset = start - vma->vm_start;
+ offset += vma->vm_pgoff << PAGE_SHIFT;
+ len = end;
+ if (len > vma->vm_end)
+ len = vma->vm_end;
+ len -= start;
+
+ /* Update start here, since vm_end will be gone too.. */
+ start = vma->vm_end;
get_file(file);
up_read(&mm->mmap_sem);
- error = do_fsync(file, 0);
+
+ error = msync_range(file, offset, len, flags & MS_SYNC);
fput(file);
if (error || start >= end)
goto out;
down_read(&mm->mmap_sem);
vma = find_vma(mm, start);
} else {
+ start = vma->vm_end;
if (start >= end) {
error = 0;
goto out_unlock;



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