Add omitted plural endings.

Documentation/chap-checkpointing.tex

@@ -277,7 +277,7 @@ The system maintains three buffers, each one the size of a segment.
 Two buffers are used to alternate, so that one is being written to
 secondary memory while the other one (the \emph{active one}) is used
 to receive pages in main memory.  The third buffer is used to read
-back and compare what was written to secondary storage.  Two counter,
+back and compare what was written to secondary storage.  Two counters,
 $M$ and $N$, each with an initial value of $0$ is kept for each of two
 ordinary segment buffers.  $M$ indicates the first free page in the
 active segment buffer, or equivalently, the number of pages that have
@@ -302,7 +302,7 @@ page, $N$ is incremented and the page is marked as writable.
 As mentioned above, when $M+N$ reaches the value corresponding to the
 number of available pages in the segment buffer, a checkpoint is
 triggered.  The initial operation of a checkpoint is called an
-\emph{atomic flip} which involves two segment buffer that we shall
+\emph{atomic flip} which involves two segment buffers that we shall
 call $A$ and $B$.  $A$ is the current active segment buffer with $M_A+N_A$
 having reached its ceiling and $B$ is the next one to be activated
 with its $M_B$ and $N_B$ equal to $0$.