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Date: Wed, 8 May 2024 10:10:43 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Barry Song <21cnbao@...il.com>, "Huang, Ying" <ying.huang@...el.com>,
Christoph Hellwig <hch@...radead.org>, chrisl@...nel.org
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
baolin.wang@...ux.alibaba.com, david@...hat.com, hanchuanhua@...o.com,
hannes@...xchg.org, hughd@...gle.com, kasong@...cent.com,
linux-kernel@...r.kernel.org, surenb@...gle.com, v-songbaohua@...o.com,
willy@...radead.org, xiang@...nel.org, yosryahmed@...gle.com,
yuzhao@...gle.com, ziy@...dia.com, "Rafael J. Wysocki" <rafael@...nel.org>,
Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>
Subject: Re: [PATCH v3 2/6] mm: remove swap_free() and always use
swap_free_nr()
On 08/05/2024 09:30, Barry Song wrote:
> On Wed, May 8, 2024 at 7:58 PM Huang, Ying <ying.huang@...el.com> wrote:
>>
>> Ryan Roberts <ryan.roberts@....com> writes:
>>
>>> On 03/05/2024 01:50, Barry Song wrote:
>>>> From: Barry Song <v-songbaohua@...o.com>
>>>>
>>>> To streamline maintenance efforts, we propose discontinuing the use of
>>>> swap_free(). Instead, we can simply invoke swap_free_nr() with nr set
>>>> to 1. This adjustment offers the advantage of enabling batch processing
>>>> within kernel/power/swap.c. Furthermore, swap_free_nr() is designed with
>>>> a bitmap consisting of only one long, resulting in overhead that can be
>>>> ignored for cases where nr equals 1.
>>>>
>>>> Suggested-by: "Huang, Ying" <ying.huang@...el.com>
>>>> Signed-off-by: Barry Song <v-songbaohua@...o.com>
>>>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
>>>> Cc: Pavel Machek <pavel@....cz>
>>>> Cc: Len Brown <len.brown@...el.com>
>>>> Cc: Hugh Dickins <hughd@...gle.com>
>>>> ---
>>>> include/linux/swap.h | 5 -----
>>>> kernel/power/swap.c | 7 +++----
>>>> mm/memory.c | 2 +-
>>>> mm/rmap.c | 4 ++--
>>>> mm/shmem.c | 4 ++--
>>>> mm/swapfile.c | 19 +++++--------------
>>>> 6 files changed, 13 insertions(+), 28 deletions(-)
>>>>
>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>>> index d1d35e92d7e9..f03cb446124e 100644
>>>> --- a/include/linux/swap.h
>>>> +++ b/include/linux/swap.h
>>>> @@ -482,7 +482,6 @@ extern int add_swap_count_continuation(swp_entry_t, gfp_t);
>>>> extern void swap_shmem_alloc(swp_entry_t);
>>>> extern int swap_duplicate(swp_entry_t);
>>>> extern int swapcache_prepare(swp_entry_t);
>>>> -extern void swap_free(swp_entry_t);
>>>
>>> I wonder if it would be cleaner to:
>>>
>>> #define swap_free(entry) swap_free_nr((entry), 1)
>>>
>>> To save all the churn for the callsites that just want to pass a single entry?
>>
>> I prefer this way. Although I prefer inline functions.
Yes, I agree inline function is the better approach.
>
> Yes, using static inline is preferable. I've recently submitted
> a checkpatch/codestyle for this, which can be found at:
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything&id=39c58d5ed036
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything&id=8379bf0b0e1f5
>
> Using static inline aligns with the established rule.
>
>>
>> Otherwise, LGTM. Feel free to add
>>
>> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
>
> Thanks!
>
>>
>> in the future version.
>
> I believe Christoph's vote leans towards simply removing swap_free_nr
> and renaming it to swap_free, while adding a new parameter as follows.
>
> void swap_free(swp_entry_t entry, int nr);
> {
> }
>
> now I see Ryan and you prefer
>
> static inline swap_free()
> {
> swap_free_nr(...., 1)
> }
>
> Chris slightly favors discouraging the use of swap_free() without the
> new parameter. Removing swap_free() can address this concern.
>
> It seems that maintaining swap_free() and having it call swap_free_nr() with
> a default value of 1 received the most support.
>
> To align with free_swap_and_cache() and free_swap_and_cache_nr(),
> I'll proceed with the "static inline" approach in the new version. Please
> voice any objections you may have, Christoph, Chris.
I'm happy with either route. If you end up adding a nr param to swap_free() then
it would also be good to give free_swap_and_cache_nr() the same treatment.
>
>>
>>>> extern void swap_free_nr(swp_entry_t entry, int nr_pages);
>>>> extern void swapcache_free_entries(swp_entry_t *entries, int n);
>>>> extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
>>>> @@ -561,10 +560,6 @@ static inline int swapcache_prepare(swp_entry_t swp)
>>>> return 0;
>>>> }
>>>>
>>>> -static inline void swap_free(swp_entry_t swp)
>>>> -{
>>>> -}
>>>> -
>>>> static inline void swap_free_nr(swp_entry_t entry, int nr_pages)
>>>> {
>>>> }
>>>> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
>>>> index 5bc04bfe2db1..6befaa88a342 100644
>>>> --- a/kernel/power/swap.c
>>>> +++ b/kernel/power/swap.c
>>>> @@ -181,7 +181,7 @@ sector_t alloc_swapdev_block(int swap)
>>>> offset = swp_offset(get_swap_page_of_type(swap));
>>>> if (offset) {
>>>> if (swsusp_extents_insert(offset))
>>>> - swap_free(swp_entry(swap, offset));
>>>> + swap_free_nr(swp_entry(swap, offset), 1);
>>>> else
>>>> return swapdev_block(swap, offset);
>>>> }
>>>> @@ -200,12 +200,11 @@ void free_all_swap_pages(int swap)
>>>>
>>>> while ((node = swsusp_extents.rb_node)) {
>>>> struct swsusp_extent *ext;
>>>> - unsigned long offset;
>>>>
>>>> ext = rb_entry(node, struct swsusp_extent, node);
>>>> rb_erase(node, &swsusp_extents);
>>>> - for (offset = ext->start; offset <= ext->end; offset++)
>>>> - swap_free(swp_entry(swap, offset));
>>>> + swap_free_nr(swp_entry(swap, ext->start),
>>>> + ext->end - ext->start + 1);
>>>>
>>>> kfree(ext);
>>>> }
>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>> index eea6e4984eae..f033eb3528ba 100644
>>>> --- a/mm/memory.c
>>>> +++ b/mm/memory.c
>>>> @@ -4225,7 +4225,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>>>> * We're already holding a reference on the page but haven't mapped it
>>>> * yet.
>>>> */
>>>> - swap_free(entry);
>>>> + swap_free_nr(entry, 1);
>>>> if (should_try_to_free_swap(folio, vma, vmf->flags))
>>>> folio_free_swap(folio);
>>>>
>>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>>> index 087a79f1f611..39ec7742acec 100644
>>>> --- a/mm/rmap.c
>>>> +++ b/mm/rmap.c
>>>> @@ -1865,7 +1865,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>>> goto walk_done_err;
>>>> }
>>>> if (arch_unmap_one(mm, vma, address, pteval) < 0) {
>>>> - swap_free(entry);
>>>> + swap_free_nr(entry, 1);
>>>> set_pte_at(mm, address, pvmw.pte, pteval);
>>>> goto walk_done_err;
>>>> }
>>>> @@ -1873,7 +1873,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>>> /* See folio_try_share_anon_rmap(): clear PTE first. */
>>>> if (anon_exclusive &&
>>>> folio_try_share_anon_rmap_pte(folio, subpage)) {
>>>> - swap_free(entry);
>>>> + swap_free_nr(entry, 1);
>>>> set_pte_at(mm, address, pvmw.pte, pteval);
>>>> goto walk_done_err;
>>>> }
>>>> diff --git a/mm/shmem.c b/mm/shmem.c
>>>> index fa2a0ed97507..bfc8a2beb24f 100644
>>>> --- a/mm/shmem.c
>>>> +++ b/mm/shmem.c
>>>> @@ -1836,7 +1836,7 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
>>>> * in shmem_evict_inode().
>>>> */
>>>> shmem_recalc_inode(inode, -1, -1);
>>>> - swap_free(swap);
>>>> + swap_free_nr(swap, 1);
>>>> }
>>>>
>>>> /*
>>>> @@ -1927,7 +1927,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
>>>>
>>>> delete_from_swap_cache(folio);
>>>> folio_mark_dirty(folio);
>>>> - swap_free(swap);
>>>> + swap_free_nr(swap, 1);
>>>> put_swap_device(si);
>>>>
>>>> *foliop = folio;
>>>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>>>> index ec12f2b9d229..ddcd0f24b9a1 100644
>>>> --- a/mm/swapfile.c
>>>> +++ b/mm/swapfile.c
>>>> @@ -1343,19 +1343,6 @@ static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
>>>> swap_range_free(p, offset, 1);
>>>> }
>>>>
>>>> -/*
>>>> - * Caller has made sure that the swap device corresponding to entry
>>>> - * is still around or has not been recycled.
>>>> - */
>>>> -void swap_free(swp_entry_t entry)
>>>> -{
>>>> - struct swap_info_struct *p;
>>>> -
>>>> - p = _swap_info_get(entry);
>>>> - if (p)
>>>> - __swap_entry_free(p, entry);
>>>> -}
>>>> -
>>>> static void cluster_swap_free_nr(struct swap_info_struct *sis,
>>>> unsigned long offset, int nr_pages)
>>>> {
>>>> @@ -1385,6 +1372,10 @@ static void cluster_swap_free_nr(struct swap_info_struct *sis,
>>>> unlock_cluster_or_swap_info(sis, ci);
>>>> }
>>>>
>>>> +/*
>>>> + * Caller has made sure that the swap device corresponding to entry
>>>> + * is still around or has not been recycled.
>>>> + */
>>>> void swap_free_nr(swp_entry_t entry, int nr_pages)
>>>> {
>>>> int nr;
>>>> @@ -1930,7 +1921,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
>>>> new_pte = pte_mkuffd_wp(new_pte);
>>>> setpte:
>>>> set_pte_at(vma->vm_mm, addr, pte, new_pte);
>>>> - swap_free(entry);
>>>> + swap_free_nr(entry, 1);
>>>> out:
>>>> if (pte)
>>>> pte_unmap_unlock(pte, ptl);
>>
>> --
>> Best Regards,
>> Huang, Ying
>
> Thanks
> Barry
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