dri2 uses the pixmap->serialNumber as a unique identifier that is
constant for the lifetime of the pixmap. (So it can detect the change of
framebuffer for example.) This appears to be the only interpretation of
pixmap->serialNumber by all the other consumers.

The result was that pageflipping was causing the DRI2 buffers to be
revoked, resulting in a massive increase in aperture thrashing - the
exact opposite of what pageflipping is supposed to achieve - under a
composting window manager.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Kristian Høgsberg <[email protected]>
Cc: Jesse Barnes <[email protected]>
---
 composite/compwindow.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/composite/compwindow.c b/composite/compwindow.c
index d2a866d..461028d 100644
--- a/composite/compwindow.c
+++ b/composite/compwindow.c
@@ -242,7 +242,6 @@ compPositionWindow (WindowPtr pWin, int x, int y)
        {
            pPixmap->screen_x = nx;
            pPixmap->screen_y = ny;
-           pPixmap->drawable.serialNumber = NEXT_SERIAL_NUMBER;
        }
     }
 
-- 
1.7.5.1

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