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Date: Wed, 8 May 2024 20:30:12 +1200
From: Barry Song <21cnbao@...il.com>
To: "Huang, Ying" <ying.huang@...el.com>, Christoph Hellwig <hch@...radead.org>, chrisl@...nel.org
Cc: Ryan Roberts <ryan.roberts@....com>, 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 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, 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.
>
> >> 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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