about BufferPoolBlowaway()

Hi, all.

I am experimenting on performance evaluation for some queries based on
PostgreSQL.
To give fair conditions to each queries, I try to clear buffer of PostgreSQL
before running each queries.
I think  the following function in .../backend/storage/buffer/bufmgr.c seems
to be designed
for such a purpose.
But the function seems to have a logical error in my opinion.

void BufferPoolBlowaway()
{
1:    int  i;

2:   BufferSync();
3:    for (i = 1; i <= NBuffers; i++)
4:   {
5:        if (BufferIsValid(i))
6:       {
7:           while (BufferIsValid(i))  ReleaseBuffer(i);
8:        }
9:       BufTableDelete(&BufferDescriptors[i - 1]);   }
}

The line 7 causes an infinite loop, I think.
So, what I did instead is the following:

void BufferPoolBlowaway()
{
1:    BufferDesc  *bufHdr;
2:    int  i;

3:    BufferSync();
4:    for (i = 1; i <= NBuffers; i++)
5:   {
6:       if (BufferIsValid(i))
7:      {
8:          bufHdr = &BufferDescriptors[i - 1];
9:          while (bufHdr->refcount > 0) ReleaseBuffer(i);
10:     }
11:     BufTableDelete(&BufferDescriptors[i - 1]);
12: }
}

Line 1, 8, and 9 are added instead of the original to release buffers.
It works without any infinite loop, but I am not quite sure that my
modification is reasonable.
Can anybody advise me about the modification?

In addition, I wonder that the disk read/write operations via buffer manager
in PostgreSQL
are free from linux system buffer cache.
If not, does anyone know how to flush and initialize the linux system buffer
cache?

Cheers.