nfs: disable data cache revalidation for swapfiles

The VM does not like PG_private set on PG_swapcache pages.  As suggested
by Trond in http://lkml.org/lkml/2006/8/25/348, this patch disables NFS
data cache revalidation on swap files.  as it does not make sense to have
other clients change the file while it is being used as swap.  This avoids
setting PG_private on swap pages, since there ought to be no further races
with invalidate_inode_pages2() to deal with.

Since we cannot set PG_private we cannot use page->private which is
already used by PG_swapcache pages to store the nfs_page.  Thus augment
the new nfs_page_find_request logic.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Paris <eparis@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Neil Brown <neilb@suse.de>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Xiaotian Feng <dfeng@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 35f7e4bc680ed1205f4d846f8649c7f77b712c20..1d57fe9f49a9e6180e535c8b71e8040d223ffd2d 100644 (file)
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -882,6 +882,10 @@ int nfs_revalidate_mapping(struct inode *inode, struct address_space *mapping)
        struct nfs_inode *nfsi = NFS_I(inode);
        int ret = 0;
 
+       /* swapfiles are not supposed to be shared. */
+       if (IS_SWAPFILE(inode))
+               goto out;
+
        if (nfs_mapping_need_revalidate_inode(inode)) {
                ret = __nfs_revalidate_inode(NFS_SERVER(inode), inode);
                if (ret < 0)

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index d0feca32b4fe3bd51f22534c4d5c09b204c7b2b7..974e9c2d31fdcfda9115cec2bb09ee61f0025af3 100644 (file)
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -139,15 +139,28 @@ static void nfs_context_set_write_error(struct nfs_open_context *ctx, int error)
        set_bit(NFS_CONTEXT_ERROR_WRITE, &ctx->flags);
 }
 
-static struct nfs_page *nfs_page_find_request_locked(struct page *page)
+static struct nfs_page *
+nfs_page_find_request_locked(struct nfs_inode *nfsi, struct page *page)
 {
        struct nfs_page *req = NULL;
 
-       if (PagePrivate(page)) {
+       if (PagePrivate(page))
                req = (struct nfs_page *)page_private(page);
-               if (req != NULL)
-                       kref_get(&req->wb_kref);
+       else if (unlikely(PageSwapCache(page))) {
+               struct nfs_page *freq, *t;
+
+               /* Linearly search the commit list for the correct req */
+               list_for_each_entry_safe(freq, t, &nfsi->commit_info.list, wb_list) {
+                       if (freq->wb_page == page) {
+                               req = freq;
+                               break;
+                       }
+               }
        }
+
+       if (req)
+               kref_get(&req->wb_kref);
+
        return req;
 }
 
@@ -157,7 +170,7 @@ static struct nfs_page *nfs_page_find_request(struct page *page)
        struct nfs_page *req = NULL;
 
        spin_lock(&inode->i_lock);
-       req = nfs_page_find_request_locked(page);
+       req = nfs_page_find_request_locked(NFS_I(inode), page);
        spin_unlock(&inode->i_lock);
        return req;
 }
@@ -258,7 +271,7 @@ static struct nfs_page *nfs_find_and_lock_request(struct page *page, bool nonblo
 
        spin_lock(&inode->i_lock);
        for (;;) {
-               req = nfs_page_find_request_locked(page);
+               req = nfs_page_find_request_locked(NFS_I(inode), page);
                if (req == NULL)
                        break;
                if (nfs_lock_request(req))
@@ -413,9 +426,15 @@ static void nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
        spin_lock(&inode->i_lock);
        if (!nfsi->npages && NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
                inode->i_version++;
-       set_bit(PG_MAPPED, &req->wb_flags);
-       SetPagePrivate(req->wb_page);
-       set_page_private(req->wb_page, (unsigned long)req);
+       /*
+        * Swap-space should not get truncated. Hence no need to plug the race
+        * with invalidate/truncate.
+        */
+       if (likely(!PageSwapCache(req->wb_page))) {
+               set_bit(PG_MAPPED, &req->wb_flags);
+               SetPagePrivate(req->wb_page);
+               set_page_private(req->wb_page, (unsigned long)req);
+       }
        nfsi->npages++;
        kref_get(&req->wb_kref);
        spin_unlock(&inode->i_lock);
@@ -432,9 +451,11 @@ static void nfs_inode_remove_request(struct nfs_page *req)
        BUG_ON (!NFS_WBACK_BUSY(req));
 
        spin_lock(&inode->i_lock);
-       set_page_private(req->wb_page, 0);
-       ClearPagePrivate(req->wb_page);
-       clear_bit(PG_MAPPED, &req->wb_flags);
+       if (likely(!PageSwapCache(req->wb_page))) {
+               set_page_private(req->wb_page, 0);
+               ClearPagePrivate(req->wb_page);
+               clear_bit(PG_MAPPED, &req->wb_flags);
+       }
        nfsi->npages--;
        spin_unlock(&inode->i_lock);
        nfs_release_request(req);
@@ -730,7 +751,7 @@ static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
        spin_lock(&inode->i_lock);
 
        for (;;) {
-               req = nfs_page_find_request_locked(page);
+               req = nfs_page_find_request_locked(NFS_I(inode), page);
                if (req == NULL)
                        goto out_unlock;
 
@@ -1744,7 +1765,7 @@ int nfs_wb_page_cancel(struct inode *inode, struct page *page)
  */
 int nfs_wb_page(struct inode *inode, struct page *page)
 {
-       loff_t range_start = page_offset(page);
+       loff_t range_start = page_file_offset(page);
        loff_t range_end = range_start + (loff_t)(PAGE_CACHE_SIZE - 1);
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,