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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [PATCH v2 4/5] ext4: improve cr 0 / cr 1 group scanning
Date:   Thu, 25 Feb 2021 21:42:54 -0700
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To:     harshad shirwadkar <harshadshirwadkar@gmail.com>
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On Feb 25, 2021, at 9:06 PM, harshad shirwadkar =
<harshadshirwadkar@gmail.com> wrote:
>=20
> Hi Andreas,
>=20
> On Thu, Feb 25, 2021 at 7:43 PM Andreas Dilger <adilger@dilger.ca> =
wrote:
>>=20
>> Yes, modulo using the existing "mb_min_to_scan" parameter for this.
>> I think 4 or 8 or 10 groups is reasonable (512MB, 1GB, 1.25GB),
>> since if it needs a seek anyway then we may as well find a good
>> group for this.
> If I understand it right, the meaning of mb_min_to_scan is the number
> of *extents* that the allocator should try to find before choosing the
> best one. However, what we want here is the number of *groups* that
> the allocator should travel linearly before trying to optimize the
> search. So, even if mb_min_to_scan is set to 1, by the current
> definition of it, it means that the allocator may still traverse the
> entire file system if it doesn't find a match. Is my understanding
> right?

Sorry, you are right.  It is the number of extents to scan and not
the number of groups.

Cheers, Andreas


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