linux-kernel - Re: [PATCH -v2 0/9] migrate

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Date:   Thu, 12 Jan 2023 16:11:43 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Zi Yan <ziy@...dia.com>,
        Yang Shi <shy828301@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Bharata B Rao <bharata@....com>,
        Alistair Popple <apopple@...dia.com>,
        haoxin <xhao@...ux.alibaba.com>
Subject: Re: [PATCH -v2 0/9] migrate_pages(): batch TLB flushing

On 01/12/23 15:17, Huang, Ying wrote:
> Mike Kravetz <mike.kravetz@...cle.com> writes:
> 
> > On 01/12/23 08:09, Huang, Ying wrote:
> >> Hi, Mike,
> >> 
> >> Mike Kravetz <mike.kravetz@...cle.com> writes:
> >> 
> >> > On 01/10/23 17:53, Mike Kravetz wrote:
> >> >> Just saw the following easily reproducible issue on next-20230110.  Have not
> >> >> verified it is related to/caused by this series, but it looks suspicious.
> >> >
> >> > Verified this is caused by the series,
> >> >
> >> > 734cbddcfe72 migrate_pages: organize stats with struct migrate_pages_stats
> >> > to
> >> > 323b933ba062 migrate_pages: batch flushing TLB
> >> >
> >> > in linux-next.
> >> 
> >> Thanks for reporting.
> >> 
> >> I tried this yesterday (next-20230111), but failed to reproduce it.  Can
> >> you share your kernel config?  Is there any other setup needed?
> >
> > Config file is attached.
> 
> Thanks!
> 
> > Are you writing a REALLY big value to nr_hugepages?  By REALLY big I
> > mean a value that is impossible to fulfill.  This will result in
> > successful hugetlb allocations until __alloc_pages starts to fail.  At
> > this point we will be stressing compaction/migration trying to find more
> > contiguous pages.
> >
> > Not sure if it matters, but I am running on a 2 node VM.  The 2 nodes
> > may be important as the hugetlb allocation code will try a little harder
> > alternating between nodes that may perhaps stress compaction/migration
> > more.
> 
> Tried again on a 2-node machine.  Still cannot reproduce it.
> 
> >> BTW: can you bisect to one specific commit which causes the bug in the
> >> series?
> >
> > I should have some time to isolate in the next day or so.

Isolated to patch,
[PATCH -v2 4/9] migrate_pages: split unmap_and_move() to _unmap() and _move()

Actually, recreated/isolated by just applying this series to v6.2-rc3 in an
effort to eliminate any possible noise in linux-next.

Spent a little time looking at modifications made there, but nothing stood out.
Will investigate more as time allows.
-- 
Mike Kravetz