linux-fsdevel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hugh Dickins <hughd@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jan Kara <jack@suse.cz>,
	William Kucharski <william.kucharski@oracle.com>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@lst.de,
	hannes@cmpxchg.org, yang.shi@linux.alibaba.com,
	dchinner@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 00/16] Overhaul multi-page lookups for THP
Date: Tue, 17 Nov 2020 08:26:03 -0800 (PST)	[thread overview]
Message-ID: <alpine.LSU.2.11.2011170820030.1014@eggly.anvils> (raw)
In-Reply-To: <20201117153947.GL29991@casper.infradead.org>

On Tue, 17 Nov 2020, Matthew Wilcox wrote:
> On Mon, Nov 16, 2020 at 02:34:34AM -0800, Hugh Dickins wrote:
> > Fix to [PATCH v4 15/16] mm/truncate,shmem: Handle truncates that split THPs.
> > One machine ran fine, swapping and building in ext4 on loop0 on huge tmpfs;
> > one machine got occasional pages of zeros in its .os; one machine couldn't
> > get started because of ext4_find_dest_de errors on the newly mkfs'ed fs.
> > The partial_end case was decided by PAGE_SIZE, when there might be a THP
> > there.  The below patch has run well (for not very long), but I could
> > easily have got it slightly wrong, off-by-one or whatever; and I have
> > not looked into the similar code in mm/truncate.c, maybe that will need
> > a similar fix or maybe not.
> 
> Thank you for the explanation in your later email!  There is indeed an
> off-by-one, although in the safe direction.
> 
> > --- 5103w/mm/shmem.c	2020-11-12 15:46:21.075254036 -0800
> > +++ 5103wh/mm/shmem.c	2020-11-16 01:09:35.431677308 -0800
> > @@ -874,7 +874,7 @@ static void shmem_undo_range(struct inod
> >  	long nr_swaps_freed = 0;
> >  	pgoff_t index;
> >  	int i;
> > -	bool partial_end;
> > +	bool same_page;
> >  
> >  	if (lend == -1)
> >  		end = -1;	/* unsigned, so actually very big */
> > @@ -907,16 +907,12 @@ static void shmem_undo_range(struct inod
> >  		index++;
> >  	}
> >  
> > -	partial_end = ((lend + 1) % PAGE_SIZE) > 0;
> > +	same_page = (lstart >> PAGE_SHIFT) == end;
> 
> 'end' is exclusive, so this is always false.  Maybe something "obvious":
> 
> 	same_page = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
> 
> (lend is inclusive, so lend in 0-4095 are all on the same page)

My brain is not yet in gear this morning, so I haven't given this the
necessary thought: but I do have to question what you say there, and
throw it back to you for the further thought -

the first shmem_getpage(inode, lstart >> PAGE_SHIFT, &page, SGP_READ);
the second shmem_getpage(inode, end, &page, SGP_READ).
So same_page = (lstart >> PAGE_SHIFT) == end
had seemed right to me.

> 
> >  	page = NULL;
> >  	shmem_getpage(inode, lstart >> PAGE_SHIFT, &page, SGP_READ);
> >  	if (page) {
> > -		bool same_page;
> > -
> >  		page = thp_head(page);
> >  		same_page = lend < page_offset(page) + thp_size(page);
> > -		if (same_page)
> > -			partial_end = false;
> >  		set_page_dirty(page);
> >  		if (!truncate_inode_partial_page(page, lstart, lend)) {
> >  			start = page->index + thp_nr_pages(page);
> > @@ -928,7 +924,7 @@ static void shmem_undo_range(struct inod
> >  		page = NULL;
> >  	}
> >  
> > -	if (partial_end)
> > +	if (!same_page)
> >  		shmem_getpage(inode, end, &page, SGP_READ);
> >  	if (page) {
> >  		page = thp_head(page);
> 

  reply	other threads:[~2020-11-17 16:26 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-12 21:26 Matthew Wilcox (Oracle)
2020-11-12 21:26 ` [PATCH v4 01/16] mm: Make pagecache tagged lookups return only head pages Matthew Wilcox (Oracle)
2020-11-14  9:53   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 02/16] mm/shmem: Use pagevec_lookup in shmem_unlock_mapping Matthew Wilcox (Oracle)
2020-11-14  9:53   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 03/16] mm/swap: Optimise get_shadow_from_swap_cache Matthew Wilcox (Oracle)
2020-11-14  9:53   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 04/16] mm: Add FGP_ENTRY Matthew Wilcox (Oracle)
2020-11-14 10:00   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 05/16] mm/filemap: Rename find_get_entry to mapping_get_entry Matthew Wilcox (Oracle)
2020-11-14 10:01   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 06/16] mm/filemap: Add helper for finding pages Matthew Wilcox (Oracle)
2020-11-14 10:03   ` Christoph Hellwig
2020-11-14 15:15     ` Matthew Wilcox
2020-11-12 21:26 ` [PATCH v4 07/16] mm/filemap: Add mapping_seek_hole_data Matthew Wilcox (Oracle)
2020-11-14 10:04   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 08/16] iomap: Use mapping_seek_hole_data Matthew Wilcox (Oracle)
2020-11-14 10:06   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 09/16] mm: Add and use find_lock_entries Matthew Wilcox (Oracle)
2020-11-14 10:07   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 10/16] mm: Add an 'end' parameter to find_get_entries Matthew Wilcox (Oracle)
2020-11-14 10:08   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 11/16] mm: Add an 'end' parameter to pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-11-14 10:19   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 12/16] mm: Remove nr_entries parameter from pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-11-14 10:19   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 13/16] mm: Pass pvec directly to find_get_entries Matthew Wilcox (Oracle)
2020-11-14 10:21   ` Christoph Hellwig
2020-11-14 15:22     ` Matthew Wilcox
2020-11-12 21:26 ` [PATCH v4 14/16] mm: Remove pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-11-14 10:22   ` Christoph Hellwig
2020-11-12 21:26 ` [PATCH v4 15/16] mm/truncate,shmem: Handle truncates that split THPs Matthew Wilcox (Oracle)
2020-11-12 21:26 ` [PATCH v4 16/16] mm/filemap: Return only head pages from find_get_entries Matthew Wilcox (Oracle)
2020-11-14 10:23   ` Christoph Hellwig
2020-11-16 10:34 ` [PATCH v4 00/16] Overhaul multi-page lookups for THP Hugh Dickins
2020-11-16 15:14   ` Matthew Wilcox
2020-11-16 21:27     ` Hugh Dickins
2020-11-17 15:39   ` Matthew Wilcox
2020-11-17 16:26     ` Hugh Dickins [this message]
2020-11-17 19:15       ` Matthew Wilcox
2020-11-17 23:43         ` Matthew Wilcox
2020-11-25  2:32           ` Matthew Wilcox
2020-11-25  2:50             ` Hugh Dickins
2020-11-25  2:56               ` Hugh Dickins
2020-11-25 23:08             ` Andrew Morton
2020-11-26  0:11               ` Hugh Dickins
2020-11-26 12:15                 ` Matthew Wilcox
2020-11-26 19:24                   ` Hugh Dickins
2020-11-26 20:07                     ` Matthew Wilcox
2020-11-30 19:45                       ` Hugh Dickins
2020-12-01  4:52                         ` Hugh Dickins
     [not found]             ` <CGME20201203154604eucas1p200d001d25dd344a1dd1c7da34f35aad0@eucas1p2.samsung.com>
2020-12-03 15:46               ` Marek Szyprowski
     [not found]                 ` <CGME20201203172725eucas1p2fddec1d269c55095859d490942b78b93@eucas1p2.samsung.com>
2020-12-03 17:27                   ` Marek Szyprowski
2020-12-03 21:27                     ` Qian Cai
2020-12-03 22:19                       ` Hugh Dickins
2020-12-03 21:45                     ` Hugh Dickins
2021-02-23 22:58 ` Andrew Morton
2021-02-23 23:27   ` Matthew Wilcox

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=alpine.LSU.2.11.2011170820030.1014@eggly.anvils \
    --to=hughd@google.com \
    --cc=akpm@linux-foundation.org \
    --cc=dchinner@redhat.com \
    --cc=hannes@cmpxchg.org \
    --cc=hch@lst.de \
    --cc=jack@suse.cz \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=william.kucharski@oracle.com \
    --cc=willy@infradead.org \
    --cc=yang.shi@linux.alibaba.com \
    --subject='Re: [PATCH v4 00/16] Overhaul multi-page lookups for THP' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox