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Re: in 3.7 kernel, how does 1GB page tables for kernel pagetables affect

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: in 3.7 kernel, how does 1GB page tables for kernel pagetables affect XFS?
From: Linda Walsh <xfs@xxxxxxxxx>
Date: Sat, 19 Jan 2013 15:55:17 -0800
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130119231644.GX2498@dastard>
References: <50FAF860.3000702@xxxxxxxxx> <20130119231644.GX2498@dastard>
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Dave Chinner wrote:
On Sat, Jan 19, 2013 at 11:47:44AM -0800, Linda Walsh wrote:
Given that XFS relies on the page size for it's maximum block size,
does switching to 1GB pages for kernel pagetables allow for larger
page-size use in XFS -- and therefore, larger blocksize?

No, it doesn't. The page cache can't use large pages so there's no
path to allowing XFS to use larger blocks with them.

As it is, you'd need a system that supports 16k or 64k page sizes
for this to be useful, otherwise you just waste a *lot* of memory...

Is it something that might be in the not too distant future? ;-)

I have no plans to do this any time soon - there's no compelling
reason to do so. I can't speak for anyone else, though...

        No prob.. I admit a 1GB page size might be a tad large for
my purposes...  I actually was reading 1MB though even that would be
large...but a GB/disk sector...um...-- at least I'd be likely to
get full speed read & writes if I could fill them...(1GB/R or W
gives me about the fastest overall throughput to my disks).

        Can't test higher (i.e. >=2GB) than that due to getting
partial block read/writes (on a 64 bit machine??)  Sounds like
my LSI controller is only 32bits...but that doesn't seem right...
Maybe it only supports consecutive read/writes up to the limit
of the memory on the controller card..

        All that talk about RAIDs recently, got me depressed a bit
when I realize that while I can get fast speeds, type speeds in seeking
around are about 1/10-1/20th the speed...sigh.

        Might that indicate that I should go with smaller RAIDS with more
spindles?  I.e. instead of 3 groups of RAID5 striped as 0, go for 4-5 groups
of RAID5 striped as a 0?  Just aligning the darn things nearly takes a rocket
scientist!  But then start talking about multiple spindles and optimizing
IOP's...ARG!...;-)  (If it wasn't challenging, I'd find it boring...)...

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