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Date: Thu, 6 Jun 2024 21:55:55 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: swap: remove 'synchronous' argument to swap_read_folio()
On Thu, Jun 6, 2024 at 6:48 PM Huang, Ying <ying.huang@...el.com> wrote:
>
> Yosry Ahmed <yosryahmed@...gle.com> writes:
>
> > swap_read_folio() reads the folio synchronously if synchronous is passed
> > as true or if SWP_SYNCHRONOUS_IO is set in swap_info_struct. The only
> > caller that passes synchronous=true is in do_swap_page() in the
> > SWP_SYNCHRONOUS_IO case.
> >
> > Hence, the argument is redundant, it is only set to true when the swap
> > read would have been synchronous anyway. Remove it.
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
>
> LGTM, Thanks!
>
> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
Thanks!
>
> And, there's some history information in commit b243dcbf2f13 ("swap:
> remove remnants of polling from read_swap_cache_async").
>
> "
> Commit [1] introduced IO polling support duding swapin to reduce swap read
> latency for block devices that can be polled. However later commit [2]
> removed polling support. Therefore it seems safe to remove do_poll
> parameter in read_swap_cache_async and always call swap_readpage with
> synchronous=false waiting for IO completion in folio_lock_or_retry.
>
> [1] commit 23955622ff8d ("swap: add block io poll in swapin path")
> [2] commit 9650b453a3d4 ("block: ignore RWF_HIPRI hint for sync dio")
> "
>
> IMO, it will help people to understand the code change to add some
> history information as above, or refer to the commit.
I sent a v2 with some history in the commit log.
>
> --
> Best Regards,
> Huang, Ying
>
> > ---
> > mm/memory.c | 2 +-
> > mm/page_io.c | 6 +++---
> > mm/swap.h | 6 ++----
> > mm/swap_state.c | 10 +++++-----
> > 4 files changed, 11 insertions(+), 13 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index db91304882312..2b3ef08e8bb7d 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -4113,7 +4113,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> >
> > /* To provide entry to swap_read_folio() */
> > folio->swap = entry;
> > - swap_read_folio(folio, true, NULL);
> > + swap_read_folio(folio, NULL);
> > folio->private = NULL;
> > }
> > } else {
> > diff --git a/mm/page_io.c b/mm/page_io.c
> > index 41e8d738c6d28..f1a9cfab6e748 100644
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> > @@ -493,10 +493,10 @@ static void swap_read_folio_bdev_async(struct folio *folio,
> > submit_bio(bio);
> > }
> >
> > -void swap_read_folio(struct folio *folio, bool synchronous,
> > - struct swap_iocb **plug)
> > +void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
> > {
> > struct swap_info_struct *sis = swp_swap_info(folio->swap);
> > + bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
> > bool workingset = folio_test_workingset(folio);
> > unsigned long pflags;
> > bool in_thrashing;
> > @@ -521,7 +521,7 @@ void swap_read_folio(struct folio *folio, bool synchronous,
> > folio_unlock(folio);
> > } else if (data_race(sis->flags & SWP_FS_OPS)) {
> > swap_read_folio_fs(folio, plug);
> > - } else if (synchronous || (sis->flags & SWP_SYNCHRONOUS_IO)) {
> > + } else if (synchronous) {
> > swap_read_folio_bdev_sync(folio, sis);
> > } else {
> > swap_read_folio_bdev_async(folio, sis);
> > diff --git a/mm/swap.h b/mm/swap.h
> > index 2c0e96272d498..baa1fa946b347 100644
> > --- a/mm/swap.h
> > +++ b/mm/swap.h
> > @@ -11,8 +11,7 @@ struct mempolicy;
> > /* linux/mm/page_io.c */
> > int sio_pool_init(void);
> > struct swap_iocb;
> > -void swap_read_folio(struct folio *folio, bool do_poll,
> > - struct swap_iocb **plug);
> > +void swap_read_folio(struct folio *folio, struct swap_iocb **plug);
> > void __swap_read_unplug(struct swap_iocb *plug);
> > static inline void swap_read_unplug(struct swap_iocb *plug)
> > {
> > @@ -83,8 +82,7 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
> > }
> > #else /* CONFIG_SWAP */
> > struct swap_iocb;
> > -static inline void swap_read_folio(struct folio *folio, bool do_poll,
> > - struct swap_iocb **plug)
> > +static inline void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
> > {
> > }
> > static inline void swap_write_unplug(struct swap_iocb *sio)
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index 0803eedeabe3d..994723cef8217 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -567,7 +567,7 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> > mpol_cond_put(mpol);
> >
> > if (page_allocated)
> > - swap_read_folio(folio, false, plug);
> > + swap_read_folio(folio, plug);
> > return folio;
> > }
> >
> > @@ -684,7 +684,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > if (!folio)
> > continue;
> > if (page_allocated) {
> > - swap_read_folio(folio, false, &splug);
> > + swap_read_folio(folio, &splug);
> > if (offset != entry_offset) {
> > folio_set_readahead(folio);
> > count_vm_event(SWAP_RA);
> > @@ -701,7 +701,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > &page_allocated, false);
> > if (unlikely(page_allocated)) {
> > zswap_folio_swapin(folio);
> > - swap_read_folio(folio, false, NULL);
> > + swap_read_folio(folio, NULL);
> > }
> > return folio;
> > }
> > @@ -834,7 +834,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
> > if (!folio)
> > continue;
> > if (page_allocated) {
> > - swap_read_folio(folio, false, &splug);
> > + swap_read_folio(folio, &splug);
> > if (addr != vmf->address) {
> > folio_set_readahead(folio);
> > count_vm_event(SWAP_RA);
> > @@ -853,7 +853,7 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
> > &page_allocated, false);
> > if (unlikely(page_allocated)) {
> > zswap_folio_swapin(folio);
> > - swap_read_folio(folio, false, NULL);
> > + swap_read_folio(folio, NULL);
> > }
> > return folio;
> > }
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