RE: doubt about 99% of the cases if the first byte of the file is cached.

Hi, Ingo

Yes, we didn't enable noatime.

But even we didn't enable noatime, LED should flash only for
1/10 second or shorter time since Linux just need to update
the access time flag of this file. it is not a big job and it shouldn't
take Linux a long time to update this filed. But we noticed the
Hard Disk LED flash for almost 2 seconds each time. So maybe
Linux is doing some large amount hard disk read/write operation
instead of just updating file access time flag.

I guess for all the sizes of files, the access time flag should be the
same. Is that correct?

Liang


-----Original Message-----
From: [email protected] [mailto:[email protected]]On Behalf
Of Ingo Molnar
Sent: Tuesday, April 23, 2002 7:12 AM
To: Liang Yang
Cc: [email protected]
Subject: RE: doubt about 99% of the cases if the first byte of the file is
cached.



On Tue, 23 Apr 2002, Liang Yang wrote:

> Yes, Hard disk LED flashes for sometime even the server received the
> request of the same 10MB file for the 3rd, 4th,5th time. [...]

do you have the 'noatime' mount-option enabled? Otherwise the atime field
will be updated on disk.

> I know how to read the first byte of a specific file(set
> req->desc.count=1 before I invoke do_generic_file_read ), but I don't
> know how to read just the last byte of file.

set in_file.f_pos to be inode->i_size-1, and use desc.count=1.

	Ingo



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