linux-kernel - Re: [PATCH RESEND v6 1/9] pagemap: Introduce ->memory

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Date:   Thu, 19 Aug 2021 01:11:52 -0700
From:   Jane Chu <jane.chu@...cle.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, dm-devel@...hat.com
Cc:     djwong@...nel.org, dan.j.williams@...el.com, david@...morbit.com,
        hch@....de, agk@...hat.com, snitzer@...hat.com,
        Jane Chu <jane.chu@...cle.com>
Subject: Re: [PATCH RESEND v6 1/9] pagemap: Introduce ->memory_failure()

Sorry, correction in line.

On 8/19/2021 12:18 AM, Jane Chu wrote:
> Hi, Shiyang,
> 
>  >  > > 1) What does it take and cost to make
>  >  > >     xfs_sb_version_hasrmapbt(&mp->m_sb) to return true?
>  >
>  > Enable rmpabt feature when making xfs filesystem
>  >     `mkfs.xfs -m rmapbt=1 /path/to/device`
>  > BTW, reflink is enabled by default.
> 
> Thanks!  I tried
> mkfs.xfs -d agcount=2,extszinherit=512,su=2m,sw=1 -m reflink=0 -m 
> rmapbt=1 -f /dev/pmem0
> 
> Again, injected a HW poison to the first page in a dax-file, had
> the poison consumed and received a SIGBUS. The result is better -
> 
> ** SIGBUS(7): canjmp=1, whichstep=0, **
> ** si_addr(0x0x7ff2d8800000), si_lsb(0x15), si_code(0x4, BUS_MCEERR_AR) **
> 
> The SIGBUS payload looks correct.
> 
> However, "dmesg" has 2048 lines on sending SIGBUS, one per 512bytes -

Actually that's one per 2MB, even though the poison is located
in pfn 0x1850600 only.

> 
> [ 7003.482326] Memory failure: 0x1850600: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7003.507956] Memory failure: 0x1850800: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7003.531681] Memory failure: 0x1850a00: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7003.554190] Memory failure: 0x1850c00: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7003.575831] Memory failure: 0x1850e00: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7003.596796] Memory failure: 0x1851000: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> ....
> [ 7045.738270] Memory failure: 0x194fe00: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7045.758885] Memory failure: 0x1950000: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7045.779495] Memory failure: 0x1950200: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> [ 7045.800106] Memory failure: 0x1950400: Sending SIGBUS to 
> fsdax_poison_v1:4109 due to hardware memory corruption
> 
> That's too much for a single process dealing with a single
> poison in a PMD page. If nothing else, given an .si_addr_lsb being 0x15,
> it doesn't make sense to send a SIGBUS per 512B block.
> 
> Could you determine the user process' mapping size from the filesystem,
> and take that as a hint to determine how many iterations to call
> mf_dax_kill_procs() ?

Sorry, scratch the 512byte stuff... the filesystem has been
notified the length of the poison blast radius, could it take clue
from that?

thanks,
-jane

> 
> thanks!
> -jane
> 
> 
>