Messages in this thread | | | Date | Fri, 04 Jul 2014 00:26:41 +0530 | From | Raghavendra K T <> | Subject | Re: [PATCH] mm readahead: Fix sys_readahead breakage by reverting 2MB limit (bug 79111) |
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On 07/04/2014 12:23 AM, Linus Torvalds wrote: > On Thu, Jul 3, 2014 at 11:38 AM, Raghavendra K T > <raghavendra.kt@linux.vnet.ibm.com> wrote: >> >> Okay, how about something like 256MB? I would be happy to send a patch >> for that change. > > I'd like to see some performance numbers. I know at least Fedora uses > "readahead()" in the startup scripts, do we have any performance > numbers for that? > > Also, I think 256MB is actually excessive. People still do have really > slow devices out there. USB-2 is still common, and drives that read at > 15MB/s are not unusual. Do we really want to do readahead() that can > take tens of seconds (and *will* take tens of seconds sycnhronously, > because the IO requests fill up). > > So I wouldn't go from 2 to 256. That seems like an excessive jump. I > was more thinking in the 4-8MB range. But even then, I think we should > always have technical reasons (ie preferably numbers) for the change, > not just randomly change it.
Okay. I 'll take some time to do the analysis. I think we also should keep in mind of possible remote readahead that would cause unnecessary penalty.
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