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Message-ID: <20240102175338.62012-7-ryncsn@gmail.com>
Date: Wed, 3 Jan 2024 01:53:35 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Chris Li <chrisl@...nel.org>,
"Huang, Ying" <ying.huang@...el.com>,
Hugh Dickins <hughd@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Matthew Wilcox <willy@...radead.org>,
Michal Hocko <mhocko@...e.com>,
Yosry Ahmed <yosryahmed@...gle.com>,
David Hildenbrand <david@...hat.com>,
linux-kernel@...r.kernel.org,
Kairui Song <kasong@...cent.com>
Subject: [PATCH v2 6/9] mm/swap: handle swapcache lookup in swapin_entry
From: Kairui Song <kasong@...cent.com>
Since all callers of swapin_entry need to check the swap cache first, we
can merge this common routine into swapin_entry, so it can be shared and
optimized later.
Also introduce a enum to better represent possible swap cache usage, and
add some comments about it, make the usage of swap cache easier to
understand.
Signed-off-by: Kairui Song <kasong@...cent.com>
---
mm/memory.c | 45 ++++++++++++++++++++-------------------------
mm/swap.h | 20 ++++++++++++++++++--
mm/swap_state.c | 22 ++++++++++++++--------
mm/swapfile.c | 21 +++++++++------------
4 files changed, 61 insertions(+), 47 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index b56254a875f8..ab6e76c95632 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3795,13 +3795,13 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
vm_fault_t do_swap_page(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
- struct folio *swapcache, *folio = NULL;
+ struct folio *swapcache = NULL, *folio;
+ enum swap_cache_result cache_result;
struct page *page;
struct swap_info_struct *si = NULL;
rmap_t rmap_flags = RMAP_NONE;
bool exclusive = false;
swp_entry_t entry;
- bool swapcached;
pte_t pte;
vm_fault_t ret = 0;
@@ -3859,31 +3859,26 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
if (unlikely(!si))
goto out;
- folio = swap_cache_get_folio(entry, vma, vmf->address);
- if (folio)
+ folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
+ vmf, &cache_result);
+ if (folio) {
page = folio_file_page(folio, swp_offset(entry));
- swapcache = folio;
-
- if (!folio) {
- folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
- vmf, &swapcached);
- if (folio) {
- page = folio_file_page(folio, swp_offset(entry));
- if (swapcached)
- swapcache = folio;
- } else {
- /*
- * Back out if somebody else faulted in this pte
- * while we released the pte lock.
- */
- vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
- vmf->address, &vmf->ptl);
- if (likely(vmf->pte &&
- pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
- ret = VM_FAULT_OOM;
- goto unlock;
- }
+ if (cache_result != SWAP_CACHE_BYPASS)
+ swapcache = folio;
+ } else {
+ /*
+ * Back out if somebody else faulted in this pte
+ * while we released the pte lock.
+ */
+ vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+ vmf->address, &vmf->ptl);
+ if (likely(vmf->pte &&
+ pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
+ ret = VM_FAULT_OOM;
+ goto unlock;
+ }
+ if (cache_result != SWAP_CACHE_HIT) {
/* Had to read the page from swap area: Major fault */
ret = VM_FAULT_MAJOR;
count_vm_event(PGMAJFAULT);
diff --git a/mm/swap.h b/mm/swap.h
index 502a2801f817..1f4cdb324bf0 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -4,6 +4,22 @@
struct mempolicy;
+/*
+ * Caller of swapin_entry may need to know the cache lookup result:
+ *
+ * SWAP_CACHE_HIT: cache hit, cached folio is retured.
+ * SWAP_CACHE_MISS: cache miss, folio is allocated, read from swap device
+ * and adde to swap cache, but still may return a cached
+ * folio if raced (check __read_swap_cache_async).
+ * SWAP_CACHE_BYPASS: cache miss, folio is new allocated and read
+ * from swap device bypassing the cache.
+ */
+enum swap_cache_result {
+ SWAP_CACHE_HIT,
+ SWAP_CACHE_MISS,
+ SWAP_CACHE_BYPASS,
+};
+
#ifdef CONFIG_SWAP
#include <linux/blk_types.h> /* for bio_end_io_t */
@@ -55,7 +71,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_flags,
struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
struct mempolicy *mpol, pgoff_t ilx);
struct folio *swapin_entry(swp_entry_t entry, gfp_t flag,
- struct vm_fault *vmf, bool *swapcached);
+ struct vm_fault *vmf, enum swap_cache_result *result);
static inline unsigned int folio_swap_flags(struct folio *folio)
{
@@ -87,7 +103,7 @@ static inline struct folio *swap_cluster_readahead(swp_entry_t entry,
}
static inline struct folio *swapin_entry(swp_entry_t swp, gfp_t gfp_mask,
- struct vm_fault *vmf, bool *swapcached)
+ struct vm_fault *vmf, enum swap_cache_result *result)
{
return NULL;
}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 66ff187aa5d3..f6f1e6f5d782 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -917,8 +917,7 @@ static struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
* @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.
+ * @result: a return value to indicate swap cache usage.
*
* Returns the struct page for entry and addr, after queueing swapin.
*
@@ -928,16 +927,22 @@ static struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
* or skip the readahead (ie, ramdisk based swap device).
*/
struct folio *swapin_entry(swp_entry_t entry, gfp_t gfp_mask,
- struct vm_fault *vmf, bool *swapcached)
+ struct vm_fault *vmf, enum swap_cache_result *result)
{
+ enum swap_cache_result cache_result;
struct mempolicy *mpol;
struct folio *folio;
pgoff_t ilx;
- bool cached;
+
+ folio = swap_cache_get_folio(entry, vmf->vma, vmf->address);
+ if (folio) {
+ cache_result = SWAP_CACHE_HIT;
+ goto done;
+ }
if (swap_use_no_readahead(swp_swap_info(entry), entry)) {
folio = swapin_direct(entry, gfp_mask, vmf);
- cached = false;
+ cache_result = SWAP_CACHE_BYPASS;
} else {
mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
if (swap_use_vma_readahead())
@@ -945,11 +950,12 @@ struct folio *swapin_entry(swp_entry_t entry, gfp_t gfp_mask,
else
folio = swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
mpol_cond_put(mpol);
- cached = true;
+ cache_result = SWAP_CACHE_MISS;
}
- if (swapcached)
- *swapcached = cached;
+done:
+ if (result)
+ *result = cache_result;
return folio;
}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index ce4e6c10dce7..5aa44de11edc 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1845,6 +1845,13 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
int ret;
pte_t ptent;
+ struct vm_fault vmf = {
+ .vma = vma,
+ .address = addr,
+ .real_address = addr,
+ .pmd = pmd,
+ };
+
if (!pte++) {
pte = pte_offset_map(pmd, addr);
if (!pte)
@@ -1864,18 +1871,8 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
pte_unmap(pte);
pte = NULL;
- folio = swap_cache_get_folio(entry, vma, addr);
- if (!folio) {
- struct vm_fault vmf = {
- .vma = vma,
- .address = addr,
- .real_address = addr,
- .pmd = pmd,
- };
-
- folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
- &vmf, NULL);
- }
+ folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
+ &vmf, NULL);
if (!folio) {
/*
* The entry could have been freed, and will not
--
2.43.0
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