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Re: [PATCH V2] Re-dirty pages on ENOSPC when converting delayed allocati

To: lachlan@xxxxxxx
Subject: Re: [PATCH V2] Re-dirty pages on ENOSPC when converting delayed allocations
From: Mark Goodwin <markgw@xxxxxxx>
Date: Wed, 12 Nov 2008 17:48:15 +1100
Cc: xfs-oss <xfs@xxxxxxxxxxx>, xfs-dev <xfs-dev@xxxxxxx>
In-reply-to: <48EB1ABD.3020503@xxxxxxx>
Organization: SGI Engineering
References: <48EB1ABD.3020503@xxxxxxx>
Reply-to: markgw@xxxxxxx
User-agent: Thunderbird 2.0.0.17 (Windows/20080914)
Could we please reach consensus on this patch? - it's been more
than a month .. and we have customers hitting it. If nobody has any
objections, we're going to take it and push it for 2.6.28.

Thanks
-- Mark

Lachlan McIlroy wrote:
If we get an error in xfs_page_state_convert() - and it's not EAGAIN - then
we throw away the dirty page without converting the delayed allocation. This
leaves delayed allocations that can never be removed and confuses code that
expects a flush of the file to clear them.  We need to re-dirty the page on
error so we can try again later or report that the flush failed.

This change is needed to handle the condition where we are at ENOSPC and we
exhaust the reserved block pool (because many transactions are executing
concurrently) and calls to xfs_trans_reserve() start failing with ENOSPC
errors.

Version 2 wont return EAGAIN from xfs_vm_writepage() and also converts an
ENOSPC error to an EAGAIN for asynchronous writeback to avoid setting an
error in the inode mapping when we don't need to.

--- a/fs/xfs/linux-2.6/xfs_aops.c    2008-10-07 17:02:04.000000000 +1000
+++ b/fs/xfs/linux-2.6/xfs_aops.c    2008-10-07 17:58:04.000000000 +1000
@@ -1147,16 +1147,6 @@ error:
    if (iohead)
        xfs_cancel_ioend(iohead);

-    /*
-     * If it's delalloc and we have nowhere to put it,
-     * throw it away, unless the lower layers told
-     * us to try again.
-     */
-    if (err != -EAGAIN) {
-        if (!unmapped)
-            block_invalidatepage(page, 0);
-        ClearPageUptodate(page);
-    }
    return err;
}

@@ -1185,7 +1175,7 @@ xfs_vm_writepage(
    struct page        *page,
    struct writeback_control *wbc)
{
-    int            error;
+    int            error = 0;
    int            need_trans;
    int            delalloc, unmapped, unwritten;
    struct inode        *inode = page->mapping->host;
@@ -1231,19 +1221,16 @@ xfs_vm_writepage(
     * to real space and flush out to disk.
     */
    error = xfs_page_state_convert(inode, page, wbc, 1, unmapped);
-    if (error == -EAGAIN)
-        goto out_fail;
    if (unlikely(error < 0))
-        goto out_unlock;
+        goto out_fail;

    return 0;

out_fail:
    redirty_page_for_writepage(wbc, page);
    unlock_page(page);
-    return 0;
-out_unlock:
-    unlock_page(page);
+    if (error == -EAGAIN)
+        error = 0;
    return error;
}

--- a/fs/xfs/xfs_iomap.c    2008-10-07 17:02:04.000000000 +1000
+++ b/fs/xfs/xfs_iomap.c    2008-10-07 17:58:04.000000000 +1000
@@ -269,6 +269,8 @@ xfs_iomap(

        error = xfs_iomap_write_allocate(ip, offset, count,
                         &imap, &nimaps);
+        if ((flags & BMAPI_TRYLOCK) && error == ENOSPC)
+            error = EAGAIN;
        break;
    }




--

 Mark Goodwin                                  markgw@xxxxxxx
 Engineering Manager for XFS and PCP    Phone: +61-3-99631937
 SGI Australian Software Group           Cell: +61-4-18969583
-------------------------------------------------------------

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