[PATCH] fix multiple mark_page_accessed called when sequentially writing a file with blocksize less than PAGE_SIZE ,which might pollute the LRU.

[Qiang Gao]

sequential write to a file with blocksize less than PAGE_SIZE  will call
mark_page_accessed multiple times,

        if (!pagevec_space(pvec))
                __pagevec_lru_add(pvec, lru);
it seems this trick fix this problem,but not quite thoroughly. there's a chance
that when another page was added to the pvec before the 14th page was
secondly mark_page_accesseded, then the 14th page was still active.



diff --git a/fs/open.c b/fs/open.c
index 9b33c0c..a418419 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -674,6 +674,13 @@ int open_check_o_direct(struct file *f)
        return 0;
 }

+
+static void
+file_w_state_init(struct file_w_state *wstat)
+{
+       wstat->prev_w_pos=-1;
+}
+
 static int do_dentry_open(struct file *f,
                          int (*open)(struct inode *, struct file *),
                          const struct cred *cred)
@@ -730,6 +737,7 @@ static int do_dentry_open(struct file *f,
        f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

        file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
+       file_w_state_init(&f->f_wstat);

        return 0;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7617ee0..b90d3ff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -746,6 +746,10 @@ struct file_ra_state {
        loff_t prev_pos;                /* Cache last read() position */
 };

+struct file_w_state {
+       loff_t prev_w_pos;
+};
+
 /*
  * Check if @index falls in the readahead windows.
  */
@@ -787,6 +791,7 @@ struct file {
        struct fown_struct      f_owner;
        const struct cred       *f_cred;
        struct file_ra_state    f_ra;
+       struct file_w_state             f_wstat;

        u64                     f_version;
 #ifdef CONFIG_SECURITY
diff --git a/mm/filemap.c b/mm/filemap.c
index 83efee7..ea144a9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2287,6 +2287,9 @@ static ssize_t generic_perform_write(struct file *file,
        long status = 0;
        ssize_t written = 0;
        unsigned int flags = 0;
+       unsigned long prev_pos=file->f_wstat.prev_w_pos;
+       unsigned long prev_off=(prev_pos & (PAGE_CACHE_SIZE -1));
+       pgoff_t prev_index=(prev_pos >> PAGE_CACHE_SHIFT);

        /*
         * Copies from kernel address space cannot fail (NFSD is a big user).
@@ -2296,12 +2299,14 @@ static ssize_t generic_perform_write(struct file *file,

        do {
                struct page *page;
+               pgoff_t index;
                unsigned long offset;   /* Offset into pagecache page */
                unsigned long bytes;    /* Bytes to write to page */
                size_t copied;          /* Bytes copied from user */
                void *fsdata;

                offset = (pos & (PAGE_CACHE_SIZE - 1));
+               index = pos >> PAGE_CACHE_SHIFT;
                bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
                                                iov_iter_count(i));

@@ -2334,7 +2339,8 @@ again:
                pagefault_enable();
                flush_dcache_page(page);

-               mark_page_accessed(page);
+               if (index != prev_index || offset != prev_off)
+                       mark_page_accessed(page);
                status = a_ops->write_end(file, mapping, pos, bytes, copied,
                                                page, fsdata);
                if (unlikely(status < 0))
@@ -2359,6 +2365,8 @@ again:
                }
                pos += copied;
                written += copied;
+               prev_index = index;
+               prev_off = offset;

                balance_dirty_pages_ratelimited(mapping);
                if (fatal_signal_pending(current)) {
@@ -2367,6 +2375,7 @@ again:
                }
        } while (iov_iter_count(i));

+       file->f_wstat.prev_w_pos=pos;
        return written ? written : status;
 }
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