Re: [PATCH 1/2] mm,swap: extract swap single page readahead into its own function

[Christoph Hellwig]

On Mon, Sep 21, 2020 at 10:01:47PM -0400, Rik van Riel wrote:
> +static struct page *swap_cluster_read_one(swp_entry_t entry,
> + unsigned long offset, gfp_t gfp_mask,
> + struct vm_area_struct *vma, unsigned long addr, bool readahead)
> +{
> + bool page_allocated;
> + struct page *page;
> +
> + page =__read_swap_cache_async(swp_entry(swp_type(entry), offset),
> +   gfp_mask, vma, addr, &page_allocated);

Missing whitespace after the "=".

> + if (!page)
> + return NULL;
> + if (page_allocated) {
> + swap_readpage(page, false);
> + if (readahead) {
> + SetPageReadahead(page);
> + count_vm_event(SWAP_RA);
> + }
> + }
> + put_page(page);
> + return page;
> +}

I think swap_vma_readahead can be switched to your new helper
pretty trivially as well, as could many of the users of
read_swap_cache_async.

[PATCH 1/2] mm,swap: extract swap single page readahead into its own function

[Rik van Riel]

Split swap single page readahead into its own function, to make
the next patch easier to read. No functional changes.

Signed-off-by: Rik van Riel 
---
 mm/swap_state.c | 40 +---
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index c16eebb81d8b..aacb9ba53f63 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -594,6 +594,28 @@ static unsigned long swapin_nr_pages(unsigned long offset)
return pages;
 }
 
+static struct page *swap_cluster_read_one(swp_entry_t entry,
+   unsigned long offset, gfp_t gfp_mask,
+   struct vm_area_struct *vma, unsigned long addr, bool readahead)
+{
+   bool page_allocated;
+   struct page *page;
+
+   page =__read_swap_cache_async(swp_entry(swp_type(entry), offset),
+ gfp_mask, vma, addr, &page_allocated);
+   if (!page)
+   return NULL;
+   if (page_allocated) {
+   swap_readpage(page, false);
+   if (readahead) {
+   SetPageReadahead(page);
+   count_vm_event(SWAP_RA);
+   }
+   }
+   put_page(page);
+   return page;
+}
+
 /**
  * swap_cluster_readahead - swap in pages in hope we need them soon
  * @entry: swap entry of this memory
@@ -615,14 +637,13 @@ static unsigned long swapin_nr_pages(unsigned long offset)
 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
struct vm_fault *vmf)
 {
-   struct page *page;
unsigned long entry_offset = swp_offset(entry);
unsigned long offset = entry_offset;
unsigned long start_offset, end_offset;
unsigned long mask;
struct swap_info_struct *si = swp_swap_info(entry);
struct blk_plug plug;
-   bool do_poll = true, page_allocated;
+   bool do_poll = true;
struct vm_area_struct *vma = vmf->vma;
unsigned long addr = vmf->address;
 
@@ -649,19 +670,8 @@ struct page *swap_cluster_readahead(swp_entry_t entry, 
gfp_t gfp_mask,
blk_start_plug(&plug);
for (offset = start_offset; offset <= end_offset ; offset++) {
/* Ok, do the async read-ahead now */
-   page = __read_swap_cache_async(
-   swp_entry(swp_type(entry), offset),
-   gfp_mask, vma, addr, &page_allocated);
-   if (!page)
-   continue;
-   if (page_allocated) {
-   swap_readpage(page, false);
-   if (offset != entry_offset) {
-   SetPageReadahead(page);
-   count_vm_event(SWAP_RA);
-   }
-   }
-   put_page(page);
+   swap_cluster_read_one(entry, offset, gfp_mask, vma, addr,
+ offset != entry_offset);
}
blk_finish_plug(&plug);
 
-- 
2.25.4