[PATCH v2 5/9] mm/swap: introduce swapin_entry for unified readahead policy
From: Kairui Song
Date: Tue Jan 02 2024 - 12:55:10 EST
From: Kairui Song <kasong@xxxxxxxxxxx>
Introduce swapin_entry which merges swapin_readahead and swapin_direct
making it the main entry for swapin pages, and use a unified swapin
policy.
This commit makes swapoff make use of this new helper and now swapping
off a 10G ZRAM (lzo-rle) is faster since readahead is skipped.
Before:
time swapoff /dev/zram0
real 0m12.337s
user 0m0.001s
sys 0m12.329s
After:
time swapoff /dev/zram0
real 0m9.728s
user 0m0.001s
sys 0m9.719s
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
mm/memory.c | 21 +++++++--------------
mm/swap.h | 16 ++++------------
mm/swap_state.c | 49 +++++++++++++++++++++++++++++++++----------------
mm/swapfile.c | 7 ++-----
4 files changed, 46 insertions(+), 47 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 0165c8cad489..b56254a875f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3801,6 +3801,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
rmap_t rmap_flags = RMAP_NONE;
bool exclusive = false;
swp_entry_t entry;
+ bool swapcached;
pte_t pte;
vm_fault_t ret = 0;
@@ -3864,21 +3865,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
swapcache = folio;
if (!folio) {
- if (data_race(si->flags & SWP_SYNCHRONOUS_IO) &&
- __swap_count(entry) == 1) {
- /* skip swapcache and readahead */
- folio = swapin_direct(entry, GFP_HIGHUSER_MOVABLE, vmf);
- if (folio)
- page = &folio->page;
+ folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
+ vmf, &swapcached);
+ if (folio) {
+ page = folio_file_page(folio, swp_offset(entry));
+ if (swapcached)
+ swapcache = folio;
} else {
- page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
- vmf);
- if (page)
- folio = page_folio(page);
- swapcache = folio;
- }
-
- if (!folio) {
/*
* Back out if somebody else faulted in this pte
* while we released the pte lock.
diff --git a/mm/swap.h b/mm/swap.h
index 83eab7b67e77..502a2801f817 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -54,10 +54,8 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_flags,
bool skip_if_exists);
struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
struct mempolicy *mpol, pgoff_t ilx);
-struct page *swapin_readahead(swp_entry_t entry, gfp_t flag,
- struct vm_fault *vmf);
-struct folio *swapin_direct(swp_entry_t entry, gfp_t flag,
- struct vm_fault *vmf);
+struct folio *swapin_entry(swp_entry_t entry, gfp_t flag,
+ struct vm_fault *vmf, bool *swapcached);
static inline unsigned int folio_swap_flags(struct folio *folio)
{
@@ -88,14 +86,8 @@ static inline struct folio *swap_cluster_readahead(swp_entry_t entry,
return NULL;
}
-struct folio *swapin_direct(swp_entry_t entry, gfp_t flag,
- struct vm_fault *vmf)
-{
- return NULL;
-}
-
-static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
- struct vm_fault *vmf)
+static inline struct folio *swapin_entry(swp_entry_t swp, gfp_t gfp_mask,
+ struct vm_fault *vmf, bool *swapcached)
{
return NULL;
}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index d39c5369da21..66ff187aa5d3 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -316,6 +316,11 @@ void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
release_pages(pages, nr);
}
+static inline bool swap_use_no_readahead(struct swap_info_struct *si, swp_entry_t entry)
+{
+ return data_race(si->flags & SWP_SYNCHRONOUS_IO) && __swap_count(entry) == 1;
+}
+
static inline bool swap_use_vma_readahead(void)
{
return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
@@ -870,8 +875,8 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
* Returns the struct folio for entry and addr after the swap entry is read
* in.
*/
-struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
- struct vm_fault *vmf)
+static struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
+ struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
struct folio *folio;
@@ -908,33 +913,45 @@ struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
}
/**
- * swapin_readahead - swap in pages in hope we need them soon
+ * swapin_entry - swap in a page from swap entry
* @entry: swap entry of this memory
* @gfp_mask: memory allocation flags
* @vmf: fault information
+ * @swapcached: pointer to a bool used as indicator if the
+ * page is swapped in through swapcache.
*
* Returns the struct page for entry and addr, after queueing swapin.
*
- * It's a main entry function for swap readahead. By the configuration,
+ * It's a main entry function for swap in. By the configuration,
* it will read ahead blocks by cluster-based(ie, physical disk based)
- * or vma-based(ie, virtual address based on faulty address) readahead.
+ * or vma-based(ie, virtual address based on faulty address) readahead,
+ * or skip the readahead (ie, ramdisk based swap device).
*/
-struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
- struct vm_fault *vmf)
+struct folio *swapin_entry(swp_entry_t entry, gfp_t gfp_mask,
+ struct vm_fault *vmf, bool *swapcached)
{
struct mempolicy *mpol;
- pgoff_t ilx;
struct folio *folio;
+ pgoff_t ilx;
+ bool cached;
- mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
- folio = swap_use_vma_readahead() ?
- swap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf) :
- swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
- mpol_cond_put(mpol);
+ if (swap_use_no_readahead(swp_swap_info(entry), entry)) {
+ folio = swapin_direct(entry, gfp_mask, vmf);
+ cached = false;
+ } else {
+ mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
+ if (swap_use_vma_readahead())
+ folio = swap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf);
+ else
+ folio = swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
+ mpol_cond_put(mpol);
+ cached = true;
+ }
- if (!folio)
- return NULL;
- return folio_file_page(folio, swp_offset(entry));
+ if (swapcached)
+ *swapcached = cached;
+
+ return folio;
}
#ifdef CONFIG_SYSFS
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f7271504aa0a..ce4e6c10dce7 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1866,7 +1866,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
folio = swap_cache_get_folio(entry, vma, addr);
if (!folio) {
- struct page *page;
struct vm_fault vmf = {
.vma = vma,
.address = addr,
@@ -1874,10 +1873,8 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
.pmd = pmd,
};
- page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
- &vmf);
- if (page)
- folio = page_folio(page);
+ folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
+ &vmf, NULL);
}
if (!folio) {
/*
--
2.43.0