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

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Date:   Thu, 19 Aug 2021 00:18:18 -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()

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 -

[ 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() ?

thanks!
-jane