Chris Li <chrisl@xxxxxxxxxx> 于2023年11月22日周三 01:18写道：
>
> On Sun, Nov 19, 2023 at 11:48 AM Kairui Song <ryncsn@xxxxxxxxx> wrote:
> >
> > From: Kairui Song <kasong@xxxxxxxxxxx>
> >
> > When a xa_value is returned by the cache lookup, keep it to be used
> > later for workingset refault check instead of doing the looking up again
> > in swapin_no_readahead.
> >
> > This does have a side effect of making swapoff also triggers workingset
> > check, but should be fine since swapoff does effect the workload in many
> > ways already.
>
> I need to sleep on it a bit to see if this will create another problem or not.
>
> >
> > Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> > ---
> > mm/swap_state.c | 10 ++++------
> > 1 file changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index e057c79fb06f..51de2a0412df 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -872,7 +872,6 @@ static struct page *swapin_no_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > {
> > struct folio *folio;
> > struct page *page;
> > - void *shadow = NULL;
> >
> > page = alloc_pages_mpol(gfp_mask, 0, mpol, ilx, numa_node_id());
> > folio = (struct folio *)page;
> > @@ -888,10 +887,6 @@ static struct page *swapin_no_readahead(swp_entry_t entry, gfp_t gfp_mask,
> >
> > mem_cgroup_swapin_uncharge_swap(entry);
> >
> > - shadow = get_shadow_from_swap_cache(entry);
> > - if (shadow)
> > - workingset_refault(folio, shadow);
> > -
> > folio_add_lru(folio);
> >
> > /* To provide entry to swap_readpage() */
> > @@ -922,11 +917,12 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > enum swap_cache_result cache_result;
> > struct swap_info_struct *si;
> > struct mempolicy *mpol;
> > + void *shadow = NULL;
> > struct folio *folio;
> > struct page *page;
> > pgoff_t ilx;
> >
> > - folio = swap_cache_get_folio(entry, vmf, NULL);
> > + folio = swap_cache_get_folio(entry, vmf, &shadow);
> > if (folio) {
> > page = folio_file_page(folio, swp_offset(entry));
> > cache_result = SWAP_CACHE_HIT;
> > @@ -938,6 +934,8 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > if (swap_use_no_readahead(si, swp_offset(entry))) {
> > page = swapin_no_readahead(entry, gfp_mask, mpol, ilx, vmf->vma->vm_mm);
> > cache_result = SWAP_CACHE_BYPASS;
> > + if (shadow)
> > + workingset_refault(page_folio(page), shadow);
>
> It is inconsistent why other flavors of readahead do not do the
> workingset_refault here.
Because of the readaheads and swapcache. Every readahead pages need to
be checked by workingset_refault with a different shadow (and so a
different xarray entry search is needed). And since other swapin path
need to insert page into swapcache, they will do extra xarray
search/insert anyway so this optimization won't work.
> I suggest keeping the workingset_refault in swapin_no_readahead() and
> pass the shadow argument in.
That sounds good to me.
