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mm: swap: clean up swap readahead
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When I see recent change of swap readahead, I am very unhappy about
current code structure which diverges two swap readahead algorithm in
do_swap_page.  This patch is to clean it up.

Main motivation is that fault handler doesn't need to be aware of
readahead algorithms but just should call swapin_readahead.

As first step, this patch cleans up a little bit but not perfect (I just
separate for review easier) so next patch will make the goal complete.

[[email protected]: do not check readahead flag with THP anon]
  Link: http://lkml.kernel.org/r/[email protected]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Huang Ying <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@minchank @torvalds
minchank authored and torvalds committed Apr 6, 2018
1 parent e830c63 commit eaf649e
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Showing 3 changed files with 62 additions and 77 deletions.
17 changes: 3 additions & 14 deletions include/linux/swap.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -424,12 +424,8 @@ extern struct page *__read_swap_cache_async(swp_entry_t, gfp_t,
bool *new_page_allocated);
extern struct page *swapin_readahead(swp_entry_t, gfp_t,
struct vm_area_struct *vma, unsigned long addr);

extern struct page *swap_readahead_detect(struct vm_fault *vmf,
struct vma_swap_readahead *swap_ra);
extern struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
struct vm_fault *vmf,
struct vma_swap_readahead *swap_ra);
struct vm_fault *vmf);

/* linux/mm/swapfile.c */
extern atomic_long_t nr_swap_pages;
Expand Down Expand Up @@ -548,15 +544,8 @@ static inline bool swap_use_vma_readahead(void)
return false;
}

static inline struct page *swap_readahead_detect(
struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
{
return NULL;
}

static inline struct page *do_swap_page_readahead(
swp_entry_t fentry, gfp_t gfp_mask,
struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
static inline struct page *do_swap_page_readahead(swp_entry_t fentry,
gfp_t gfp_mask, struct vm_fault *vmf)
{
return NULL;
}
Expand Down
26 changes: 6 additions & 20 deletions mm/memory.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2883,26 +2883,16 @@ EXPORT_SYMBOL(unmap_mapping_range);
int do_swap_page(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
struct page *page = NULL, *swapcache = NULL;
struct page *page = NULL, *swapcache;
struct mem_cgroup *memcg;
struct vma_swap_readahead swap_ra;
swp_entry_t entry;
pte_t pte;
int locked;
int exclusive = 0;
int ret = 0;
bool vma_readahead = swap_use_vma_readahead();

if (vma_readahead) {
page = swap_readahead_detect(vmf, &swap_ra);
swapcache = page;
}

if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) {
if (page)
put_page(page);
if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
goto out;
}

entry = pte_to_swp_entry(vmf->orig_pte);
if (unlikely(non_swap_entry(entry))) {
Expand All @@ -2928,11 +2918,8 @@ int do_swap_page(struct vm_fault *vmf)


delayacct_set_flag(DELAYACCT_PF_SWAPIN);
if (!page) {
page = lookup_swap_cache(entry, vma_readahead ? vma : NULL,
vmf->address);
swapcache = page;
}
page = lookup_swap_cache(entry, vma, vmf->address);
swapcache = page;

if (!page) {
struct swap_info_struct *si = swp_swap_info(entry);
Expand All @@ -2949,9 +2936,9 @@ int do_swap_page(struct vm_fault *vmf)
swap_readpage(page, true);
}
} else {
if (vma_readahead)
if (swap_use_vma_readahead())
page = do_swap_page_readahead(entry,
GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
GFP_HIGHUSER_MOVABLE, vmf);
else
page = swapin_readahead(entry,
GFP_HIGHUSER_MOVABLE, vma, vmf->address);
Expand Down Expand Up @@ -2982,7 +2969,6 @@ int do_swap_page(struct vm_fault *vmf)
*/
ret = VM_FAULT_HWPOISON;
delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
swapcache = page;
goto out_release;
}

Expand Down
96 changes: 53 additions & 43 deletions mm/swap_state.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -332,32 +332,43 @@ struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
unsigned long addr)
{
struct page *page;
unsigned long ra_info;
int win, hits, readahead;

page = find_get_page(swap_address_space(entry), swp_offset(entry));

INC_CACHE_INFO(find_total);
if (page) {
bool vma_ra = swap_use_vma_readahead();
bool readahead;

INC_CACHE_INFO(find_success);
/*
* At the moment, we don't support PG_readahead for anon THP
* so let's bail out rather than confusing the readahead stat.
*/
if (unlikely(PageTransCompound(page)))
return page;

readahead = TestClearPageReadahead(page);
if (vma) {
ra_info = GET_SWAP_RA_VAL(vma);
win = SWAP_RA_WIN(ra_info);
hits = SWAP_RA_HITS(ra_info);
if (vma && vma_ra) {
unsigned long ra_val;
int win, hits;

ra_val = GET_SWAP_RA_VAL(vma);
win = SWAP_RA_WIN(ra_val);
hits = SWAP_RA_HITS(ra_val);
if (readahead)
hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
atomic_long_set(&vma->swap_readahead_info,
SWAP_RA_VAL(addr, win, hits));
}

if (readahead) {
count_vm_event(SWAP_RA_HIT);
if (!vma)
if (!vma || !vma_ra)
atomic_inc(&swapin_readahead_hits);
}
}

return page;
}

Expand Down Expand Up @@ -586,8 +597,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
continue;
if (page_allocated) {
swap_readpage(page, false);
if (offset != entry_offset &&
likely(!PageTransCompound(page))) {
if (offset != entry_offset) {
SetPageReadahead(page);
count_vm_event(SWAP_RA);
}
Expand Down Expand Up @@ -649,16 +659,15 @@ static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
}

struct page *swap_readahead_detect(struct vm_fault *vmf,
struct vma_swap_readahead *swap_ra)
static void swap_ra_info(struct vm_fault *vmf,
struct vma_swap_readahead *ra_info)
{
struct vm_area_struct *vma = vmf->vma;
unsigned long swap_ra_info;
struct page *page;
unsigned long ra_val;
swp_entry_t entry;
unsigned long faddr, pfn, fpfn;
unsigned long start, end;
pte_t *pte;
pte_t *pte, *orig_pte;
unsigned int max_win, hits, prev_win, win, left;
#ifndef CONFIG_64BIT
pte_t *tpte;
Expand All @@ -667,30 +676,32 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
SWAP_RA_ORDER_CEILING);
if (max_win == 1) {
swap_ra->win = 1;
return NULL;
ra_info->win = 1;
return;
}

faddr = vmf->address;
entry = pte_to_swp_entry(vmf->orig_pte);
if ((unlikely(non_swap_entry(entry))))
return NULL;
page = lookup_swap_cache(entry, vma, faddr);
if (page)
return page;
orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
entry = pte_to_swp_entry(*pte);
if ((unlikely(non_swap_entry(entry)))) {
pte_unmap(orig_pte);
return;
}

fpfn = PFN_DOWN(faddr);
swap_ra_info = GET_SWAP_RA_VAL(vma);
pfn = PFN_DOWN(SWAP_RA_ADDR(swap_ra_info));
prev_win = SWAP_RA_WIN(swap_ra_info);
hits = SWAP_RA_HITS(swap_ra_info);
swap_ra->win = win = __swapin_nr_pages(pfn, fpfn, hits,
ra_val = GET_SWAP_RA_VAL(vma);
pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
prev_win = SWAP_RA_WIN(ra_val);
hits = SWAP_RA_HITS(ra_val);
ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
max_win, prev_win);
atomic_long_set(&vma->swap_readahead_info,
SWAP_RA_VAL(faddr, win, 0));

if (win == 1)
return NULL;
if (win == 1) {
pte_unmap(orig_pte);
return;
}

/* Copy the PTEs because the page table may be unmapped */
if (fpfn == pfn + 1)
Expand All @@ -703,23 +714,21 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
&start, &end);
}
swap_ra->nr_pte = end - start;
swap_ra->offset = fpfn - start;
pte = vmf->pte - swap_ra->offset;
ra_info->nr_pte = end - start;
ra_info->offset = fpfn - start;
pte -= ra_info->offset;
#ifdef CONFIG_64BIT
swap_ra->ptes = pte;
ra_info->ptes = pte;
#else
tpte = swap_ra->ptes;
tpte = ra_info->ptes;
for (pfn = start; pfn != end; pfn++)
*tpte++ = *pte++;
#endif

return NULL;
pte_unmap(orig_pte);
}

struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
struct vm_fault *vmf,
struct vma_swap_readahead *swap_ra)
struct vm_fault *vmf)
{
struct blk_plug plug;
struct vm_area_struct *vma = vmf->vma;
Expand All @@ -728,12 +737,14 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
swp_entry_t entry;
unsigned int i;
bool page_allocated;
struct vma_swap_readahead ra_info = {0,};

if (swap_ra->win == 1)
swap_ra_info(vmf, &ra_info);
if (ra_info.win == 1)
goto skip;

blk_start_plug(&plug);
for (i = 0, pte = swap_ra->ptes; i < swap_ra->nr_pte;
for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
i++, pte++) {
pentry = *pte;
if (pte_none(pentry))
Expand All @@ -749,8 +760,7 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
continue;
if (page_allocated) {
swap_readpage(page, false);
if (i != swap_ra->offset &&
likely(!PageTransCompound(page))) {
if (i != ra_info.offset) {
SetPageReadahead(page);
count_vm_event(SWAP_RA);
}
Expand All @@ -761,7 +771,7 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
lru_add_drain();
skip:
return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
swap_ra->win == 1);
ra_info.win == 1);
}

#ifdef CONFIG_SYSFS
Expand Down

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