2010-02-22 23:32:35

by Oliver Neukum

Subject: question on readahead and sync mounting

Hi,

if a filesystem is mounted with -osync will any readahead be done for
that filesystem?

Regards
Oliver

2010-02-22 23:59:26

by Oliver Neukum

Subject: Re: question on readahead and sync mounting

Am Dienstag, 23. Februar 2010 00:48:39 schrieben Sie:
> Please, Refer to below articles to understand readahead essentially.
>
> http://lwn.net/Articles/235164/ (On-demand readahead by corbet)
> http://kernelnewbies.org/Linux_2_6_23#head-102af265937262a7a21766ae58fddc1a29a5d8d7(
> On-demand read-ahead on Linux 2.6.23)

OK, I am looking for a way to make sure read requests on a SCSI drive
actually hit the bus after a certain event. Is there a way to do this without
tossing away the whole cache?

Regards
Oliver

2010-02-23 17:38:51

by Jeff Moyer

Subject: Re: question on readahead and sync mounting

Oliver Neukum <[email protected]> writes:

> Am Dienstag, 23. Februar 2010 00:48:39 schrieben Sie:
>> Please, Refer to below articles to understand readahead essentially.
>>
>> http://lwn.net/Articles/235164/ (On-demand readahead by corbet)
>> http://kernelnewbies.org/Linux_2_6_23#head-102af265937262a7a21766ae58fddc1a29a5d8d7(
>> On-demand read-ahead on Linux 2.6.23)
>
> OK, I am looking for a way to make sure read requests on a SCSI drive
> actually hit the bus after a certain event. Is there a way to do this without
> tossing away the whole cache?

I'm not sure I understand what you're asking, but it sounds like you
want to do an O_DIRECT read. Open the file with O_DIRECT, then pass
a properly-aligned buffer to the read(2) call.

Cheers,
Jeff