Kairui Song <ryncsn@xxxxxxxxx> writes:
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> Currently VMA readahead is globally disabled when any rotate disk is
> used as swap backend. So multiple swap devices are enabled, if a slower
> hard disk is set as a low priority fallback, and a high performance SSD
> is used and high priority swap device, vma readahead is disabled globally.
> The SSD swap device performance will drop by a lot.
>
> Check readahead policy per entry to avoid such problem.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> ---
> mm/swap_state.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index ff6756f2e8e4..fb78f7f18ed7 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -321,9 +321,9 @@ static inline bool swap_use_no_readahead(struct swap_info_struct *si, swp_entry_
> return data_race(si->flags & SWP_SYNCHRONOUS_IO) && __swap_count(entry) == 1;
> }
>
> -static inline bool swap_use_vma_readahead(void)
> +static inline bool swap_use_vma_readahead(struct swap_info_struct *si)
> {
> - return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
> + return data_race(si->flags & SWP_SOLIDSTATE) && READ_ONCE(enable_vma_readahead);
> }
>
> /*
> @@ -341,7 +341,7 @@ struct folio *swap_cache_get_folio(swp_entry_t entry,
>
> folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry));
> if (!IS_ERR(folio)) {
> - bool vma_ra = swap_use_vma_readahead();
> + bool vma_ra = swap_use_vma_readahead(swp_swap_info(entry));
> bool readahead;
>
> /*
> @@ -920,16 +920,18 @@ static struct page *swapin_no_readahead(swp_entry_t entry, gfp_t gfp_mask,
> struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
> struct vm_fault *vmf, bool *swapcached)
> {
> + struct swap_info_struct *si;
> struct mempolicy *mpol;
> struct page *page;
> pgoff_t ilx;
> bool cached;
>
> + si = swp_swap_info(entry);
> mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
> - if (swap_use_no_readahead(swp_swap_info(entry), entry)) {
> + if (swap_use_no_readahead(si, entry)) {
> page = swapin_no_readahead(entry, gfp_mask, mpol, ilx, vmf->vma->vm_mm);
> cached = false;
> - } else if (swap_use_vma_readahead()) {
> + } else if (swap_use_vma_readahead(si)) {
It's possible that some pages are swapped out to SSD while others are
swapped out to HDD in a readahead window.
I suspect that there are practical requirements to use swap on SSD and
HDD at the same time.
> page = swap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf);
> cached = true;
> } else {
--
Best Regards,
Huang, Ying
