linux-kernel - Re: [PATCH v9 4/8] hugetlb: disable region_add file

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Message-ID: <7fb223ea-3e99-550b-d19c-1352de0d296d@oracle.com>
Date:   Tue, 21 Jan 2020 09:40:56 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Mina Almasry <almasrymina@...gle.com>
Cc:     shuah@...nel.org, rientjes@...gle.com, shakeelb@...gle.com,
        gthelen@...gle.com, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, cgroups@...r.kernel.org,
        aneesh.kumar@...ux.vnet.ibm.com, mkoutny@...e.com
Subject: Re: [PATCH v9 4/8] hugetlb: disable region_add file_region coalescing

On 1/21/20 9:38 AM, Mike Kravetz wrote:
> On 12/17/19 3:16 PM, Mina Almasry wrote:
>> A follow up patch in this series adds hugetlb cgroup uncharge info the
> 
> *nit*
> A follow up patch in this series adds hugetlb cgroup uncharge info to the
> 
>> file_region entries in resv->regions. The cgroup uncharge info may
>> differ for different regions, so they can no longer be coalesced at
>> region_add time. So, disable region coalescing in region_add in this
>> patch.
>>
>> Behavior change:
>>
>> Say a resv_map exists like this [0->1], [2->3], and [5->6].
>>
>> Then a region_chg/add call comes in region_chg/add(f=0, t=5).
>>
>> Old code would generate resv->regions: [0->5], [5->6].
>> New code would generate resv->regions: [0->1], [1->2], [2->3], [3->5],
>> [5->6].
>>
>> Special care needs to be taken to handle the resv->adds_in_progress
>> variable correctly. In the past, only 1 region would be added for every
>> region_chg and region_add call. But now, each call may add multiple
>> regions, so we can no longer increment adds_in_progress by 1 in region_chg,
>> or decrement adds_in_progress by 1 after region_add or region_abort. Instead,
>> region_chg calls add_reservation_in_range() to count the number of regions
>> needed and allocates those, and that info is passed to region_add and
>> region_abort to decrement adds_in_progress correctly.
>>
>> We've also modified the assumption that region_add after region_chg
>> never fails. region_chg now pre-allocates at least 1 region for
>> region_add. If region_add needs more regions than region_chg has
>> allocated for it, then it may fail.
>>
>> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> 
> Thanks for the updated comments.  Still,
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>


Sorry, that comment was directed at V10 of the patch.

-- 
Mike Kravetz