linux-kernel - Re: [PATCH v12 00/10] enable bs

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Message-ID: <3405743.1724068772@warthog.procyon.org.uk>
Date: Mon, 19 Aug 2024 12:59:32 +0100
From: David Howells <dhowells@...hat.com>
Cc: dhowells@...hat.com,
    "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
    brauner@...nel.org, akpm@...ux-foundation.org,
    chandan.babu@...cle.com, linux-fsdevel@...r.kernel.org,
    djwong@...nel.org, hare@...e.de, gost.dev@...sung.com,
    linux-xfs@...r.kernel.org, hch@....de, david@...morbit.com,
    Zi Yan <ziy@...dia.com>, yang@...amperecomputing.com,
    linux-kernel@...r.kernel.org, linux-mm@...ck.org,
    willy@...radead.org, john.g.garry@...cle.com,
    cl@...amperecomputing.com, p.raghav@...sung.com, mcgrof@...nel.org,
    ryan.roberts@....com
Subject: Re: [PATCH v12 00/10] enable bs > ps in XFS

David Howells <dhowells@...hat.com> wrote:

> You can see the invalidate_folio call, with the offset at 0x4 an the length as
> 0x1ffc.  The data at the beginning of the page is 0x78787878.  This looks
> correct.
> 
> Then second ftruncate() is called to increase the file size to 4096
> (ie. 0x1000):
> 
>  pankaj-5833: netfs_truncate: ni=9e isz=4 rsz=4 zp=4 to=1000
>  pankaj-5833: netfs_inval_folio: pfn=116fec i=0009e ix=00000-00001 o=1000 l=1000 d=78787878
>  pankaj-5833: netfs_folio: pfn=116fec i=0009e ix=00000-00001 inval-part
>  pankaj-5833: netfs_set_size: ni=9e resize-file isz=1000 rsz=1000 zp=4
> 
> And here's the problem: in the invalidate_folio() call, the offset is 0x1000
> and the length is 0x1000 (o= and l=).  But that's the wrong half of the folio!
> I'm guessing that the caller thereafter clears the other half of the folio -
> the bit that should be kept.

Actually, I think I'm wrong in my evaluation - I think that's the region to be
invalidated, not the region to be kept.

David