Problem with gridview Paging

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C#

ASP.NET

C#4.0

Gridview

paging

I use linq to sql,and use a drop down for showing records,

I use this code for paging in .aspx file

<asp:DropDownList ID="drpPageSize" class="form-control" runat="server" AutoPostBack="True" OnSelectedIndexChanged="drpPageSize_SelectedIndexChanged" meta:resourcekey="drpPageSizeResource1">

   <asp:ListItem Selected="True" meta:resourcekey="ListItemResource1">5</asp:ListItem>
   <asp:ListItem meta:resourcekey="ListItemResource2">10</asp:ListItem>
   <asp:ListItem meta:resourcekey="ListItemResource10">50</asp:ListItem>
   <asp:ListItem meta:resourcekey="ListItemResource12">100</asp:ListItem>
   <asp:ListItem  Text="All" meta:resourcekey="ListItemResource11"></asp:ListItem>
</asp:DropDownList>

and use this code for .cs file,here is both code for gridbind and drpselect index changed event

protected void grdBind()
{
   try
   {
      EventManagerDataContext db = new EventManagerDataContext();

      var q = from a in db.EMR_EVENTs
      join b in db.EMR_CLIENTs on a.ClientID equals b.ClientID
      // join c in db.EMR_INVITATIONs on a.EventID equals c.EventID

      select new
      {
         ClientName = b.Name,
         ClientID = a.ClientID,
         Name = a.Name,
         No_Of_Invitees = a.No_Of_Invitees,
         Extra_Invitees = a.Extra_Invitees,
         Total_Invitees = a.Extra_Invitees + a.No_Of_Invitees,
         EventID = a.EventID,
         // InvitationId=c.InvitationID
      };

      grid.DataSource = q.ToList();
      if (Convert.ToInt32(Session["k"])== 1)
      {
         grid.PageSize = Convert.ToInt32(Session["total"]); //here total is the no of rows in gridview
      }
      else
      {
         grid.PageSize = int.Parse(drpPageSize.SelectedValue);
      }
      grid.DataBind();
   }
   catch
   {
      throw;
   }
}

protected void drpPageSize_SelectedIndexChanged(object sender, EventArgs e)
{
   if (drpPageSize.SelectedIndex == 4)
   {
      grid.AllowPaging = false;
      Session["k"] = 1;
      // grid.PageSize = Convert.ToInt32(Session["total"]);
      grdBind();
   }
   else
   {
      Session["k"] = 2;
      grid.PageSize = int.Parse(drpPageSize.SelectedItem.Text);
      grdBind();
   }
}

my all code is working. but i found that when i select all from gridview i found all records,but after select all from drop down i select 5 then i not get the 5 records ,insted of i get all the records,same as in 10,50,100

any solution please.?

i also appreciate that a better code for my requirement,my main purpose is show all records from gridview while i select all from dropdown.