From: Hugh Dickins <hughd@google.com>
To: Zi Yan <ziy@nvidia.com>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Qi Zheng <zhengqi.arch@bytedance.com>,
Yang Shi <shy828301@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Xu <peterx@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
Alistair Popple <apopple@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Ira Weiny <ira.weiny@intel.com>,
Steven Price <steven.price@arm.com>,
SeongJae Park <sj@kernel.org>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Huang Ying <ying.huang@intel.com>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Zack Rusin <zackr@vmware.com>, Jason Gunthorpe <jgg@ziepe.ca>,
Axel Rasmussen <axelrasmussen@google.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Minchan Kim <minchan@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Song Liu <song@kernel.org>,
Thomas Hellstrom <thomas.hellstrom@linux.intel.com>,
Ryan Roberts <ryan.roberts@arm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 05/32] mm/filemap: allow pte_offset_map_lock() to fail
Date: Mon, 10 Jul 2023 22:21:16 -0700 (PDT) [thread overview]
Message-ID: <7df13a2d-1c95-c753-da64-4a47e8872fd9@google.com> (raw)
In-Reply-To: <68C1B34D-B8B7-4151-B780-5A05812F402C@nvidia.com>
On Mon, 10 Jul 2023, Zi Yan wrote:
> On 8 Jun 2023, at 21:11, Hugh Dickins wrote:
>
> > filemap_map_pages() allow pte_offset_map_lock() to fail; and remove the
> > pmd_devmap_trans_unstable() check from filemap_map_pmd(), which can safely
> > return to filemap_map_pages() and let pte_offset_map_lock() discover that.
> >
> > Signed-off-by: Hugh Dickins <hughd@google.com>
> > ---
> > mm/filemap.c | 12 +++++-------
> > 1 file changed, 5 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 28b42ee848a4..9e129ad43e0d 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -3408,13 +3408,6 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
> > if (pmd_none(*vmf->pmd))
> > pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
> >
> > - /* See comment in handle_pte_fault() */
> > - if (pmd_devmap_trans_unstable(vmf->pmd)) {
> > - folio_unlock(folio);
> > - folio_put(folio);
> > - return true;
> > - }
> > -
>
> There is a pmd_trans_huge() check at the beginning, should it be removed
> as well? Since pte_offset_map_lock() is also able to detect it.
It probably could be removed: but mostly I avoided such cleanups,
in the hope that the patches could be more easily reviewed as safe.
But I was eager to delete that obscure pmd_devmap_trans_unstable().
The whole strategy of dealing with the pmd_trans_huge()-like cases first,
and only finally arriving at the pte_offset_map_lock() when other cases
have been excluded, could be reversed in *many* places. It had to be that
way before, because pte_offset_map_lock() could only cope with a page
table; but now we could reverse them to do the pte_offset_map_lock()
first, and only try the other cases when it fails.
That would in theory be more efficient; but whether measurably more
efficient I doubt. And very easy to introduce errors on the way:
my enthusiasm for such cleanups is low! But maybe there's a few
places where the rearrangement would be worthwhile.
>
> > return false;
> > }
> >
> > @@ -3501,6 +3494,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
> >
> > addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> > vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
> > + if (!vmf->pte) {
> > + folio_unlock(folio);
> > + folio_put(folio);
> > + goto out;
> > + }
> > do {
> > again:
> > page = folio_file_page(folio, xas.xa_index);
> > --
> > 2.35.3
>
> These two changes affect the ret value. Before, pmd_devmap_trans_unstable() == true
> made ret = VM_FAULT_NPAGE, but now ret is the default 0 value. So ret should be set
> to VM_FAULT_NPAGE before goto out in the second hunk?
Qi Zheng raised a similar question on the original posting, I answered
https://lore.kernel.org/linux-mm/fb9a9d57-dbd7-6a6e-d1cb-8dcd64c829a6@google.com/
It's a rare case to fault here, then find pmd_devmap(*pmd), and it really
doesn't matter whether we return VM_FAULT_NOPAGE or 0 for it - maybe I've
left it inconsistent between THP and devmap, but it doesn't really matter.
I haven't checked Matthew's v5 "new page table range API" posted today,
but I expect this all looks different here anyway.
Thanks a lot for checking these: they are now in 6.5-rc1, so if you find
something that needs fixing, all the more important that we do fix it.
Hugh
next prev parent reply other threads:[~2023-07-11 5:21 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-09 0:54 [PATCH v2 00/32] mm: allow pte_offset_map[_lock]() to fail Hugh Dickins
2023-06-09 1:06 ` [PATCH v2 01/32] mm: use pmdp_get_lockless() without surplus barrier() Hugh Dickins
2023-06-09 1:08 ` [PATCH v2 02/32] mm/migrate: remove cruft from migration_entry_wait()s Hugh Dickins
2023-06-09 1:09 ` [PATCH v2 03/32] mm/pgtable: kmap_local_page() instead of kmap_atomic() Hugh Dickins
2023-06-09 1:10 ` [PATCH v2 04/32] mm/pgtable: allow pte_offset_map[_lock]() to fail Hugh Dickins
2023-07-11 1:23 ` Zi Yan
2023-07-28 13:53 ` Yongqin Liu
2023-07-28 14:05 ` Matthew Wilcox
2023-07-28 16:58 ` Hugh Dickins
2023-08-05 16:06 ` Yongqin Liu
2023-08-05 17:07 ` Matthew Wilcox
2023-08-08 0:29 ` John Hubbard
2023-06-09 1:11 ` [PATCH v2 05/32] mm/filemap: allow pte_offset_map_lock() " Hugh Dickins
2023-07-11 1:34 ` Zi Yan
2023-07-11 5:21 ` Hugh Dickins [this message]
2023-06-09 1:12 ` [PATCH v2 06/32] mm/page_vma_mapped: delete bogosity in page_vma_mapped_walk() Hugh Dickins
2023-07-11 1:47 ` Zi Yan
2023-06-09 1:14 ` [PATCH v2 07/32] mm/page_vma_mapped: reformat map_pte() with less indentation Hugh Dickins
2023-07-11 1:56 ` Zi Yan
2023-06-09 1:15 ` [PATCH v2 08/32] mm/page_vma_mapped: pte_offset_map_nolock() not pte_lockptr() Hugh Dickins
2023-06-09 1:17 ` [PATCH v2 09/32] mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails Hugh Dickins
2023-06-09 1:18 ` [PATCH v2 10/32] mm/pagewalk: walk_pte_range() allow for pte_offset_map() Hugh Dickins
2023-06-09 1:20 ` [PATCH v2 11/32] mm/vmwgfx: simplify pmd & pud mapping dirty helpers Hugh Dickins
2023-06-09 1:21 ` [PATCH v2 12/32] mm/vmalloc: vmalloc_to_page() use pte_offset_kernel() Hugh Dickins
2023-07-10 14:42 ` Mark Brown
2023-07-10 17:18 ` Lorenzo Stoakes
2023-07-10 17:33 ` Mark Brown
2023-07-11 4:34 ` Hugh Dickins
2023-07-11 15:34 ` Mark Brown
2023-07-11 16:13 ` Hugh Dickins
2023-07-11 16:34 ` Mark Brown
2023-07-11 17:57 ` Mark Brown
2023-07-13 11:19 ` Linux regression tracking #update (Thorsten Leemhuis)
2023-07-20 10:32 ` Will Deacon
2023-07-20 12:06 ` Mark Brown
2023-08-08 5:52 ` Linux regression tracking (Thorsten Leemhuis)
2023-08-08 11:09 ` Mark Brown
2023-08-11 8:00 ` Linux regression tracking #update (Thorsten Leemhuis)
2023-07-11 14:48 ` Linux regression tracking #adding (Thorsten Leemhuis)
2023-06-09 1:23 ` [PATCH v2 13/32] mm/hmm: retry if pte_offset_map() fails Hugh Dickins
2023-06-09 1:24 ` [PATCH v2 14/32] mm/userfaultfd: " Hugh Dickins
2023-06-09 1:26 ` [PATCH v2 15/32] mm/userfaultfd: allow pte_offset_map_lock() to fail Hugh Dickins
2023-06-09 1:27 ` [PATCH v2 16/32] mm/debug_vm_pgtable,page_table_check: warn pte map fails Hugh Dickins
2023-06-09 1:29 ` [PATCH v2 17/32] mm/various: give up if pte_offset_map[_lock]() fails Hugh Dickins
2023-06-09 1:30 ` [PATCH v2 18/32] mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge() Hugh Dickins
2023-06-09 1:32 ` [PATCH v2 19/32] mm/mremap: retry if either pte_offset_map_*lock() fails Hugh Dickins
2023-06-09 1:34 ` [PATCH v2 20/32] mm/madvise: clean up pte_offset_map_lock() scans Hugh Dickins
2023-06-09 1:35 ` [PATCH v2 21/32] mm/madvise: clean up force_shm_swapin_readahead() Hugh Dickins
2023-06-09 1:36 ` [PATCH v2 22/32] mm/swapoff: allow pte_offset_map[_lock]() to fail Hugh Dickins
2023-06-09 1:37 ` [PATCH v2 23/32] mm/mglru: allow pte_offset_map_nolock() " Hugh Dickins
2023-06-09 1:38 ` [PATCH v2 24/32] mm/migrate_device: allow pte_offset_map_lock() " Hugh Dickins
2023-06-09 1:39 ` [PATCH v2 25/32] mm/gup: remove FOLL_SPLIT_PMD use of pmd_trans_unstable() Hugh Dickins
2023-06-09 18:24 ` Yang Shi
2023-06-09 1:41 ` [PATCH v2 26/32] mm/huge_memory: split huge pmd under one pte_offset_map() Hugh Dickins
2023-06-09 1:42 ` [PATCH v2 27/32] mm/khugepaged: allow pte_offset_map[_lock]() to fail Hugh Dickins
2023-06-09 1:43 ` [PATCH v2 28/32] mm/memory: " Hugh Dickins
2023-06-09 20:06 ` Andrew Morton
2023-06-09 20:11 ` Hugh Dickins
2023-06-12 9:10 ` Ryan Roberts
2023-06-15 23:10 ` [PATCH v2 28/32 fix] mm/memory: allow pte_offset_map[_lock]() to fail: fix Hugh Dickins
2023-06-09 1:45 ` [PATCH v2 29/32] mm/memory: handle_pte_fault() use pte_offset_map_nolock() Hugh Dickins
2023-06-09 1:50 ` [PATCH v2 30/32] mm/pgtable: delete pmd_trans_unstable() and friends Hugh Dickins
2023-06-09 1:52 ` [PATCH v2 31/32] mm/swap: swap_vma_readahead() do the pte_offset_map() Hugh Dickins
2023-06-12 8:03 ` Huang, Ying
2023-06-14 3:58 ` Hugh Dickins
2023-06-09 1:53 ` [PATCH v2 32/32] perf/core: Allow pte_offset_map() to fail Hugh Dickins
2023-06-20 6:50 ` [PATCH] mm/swapfile: delete outdated pte_offset_map() comment Hugh Dickins
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