Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
On Fri 07-12-18 10:57:50, Jan Kara wrote: > On Fri 30-11-18 14:58:10, Josef Bacik wrote: > > If we do not have a page at filemap_fault time we'll do this weird > > forced page_cache_read thing to populate the page, and then drop it > > again and loop around and find it. This makes for 2 ways we can read a > > page in filemap_fault, and it's not really needed. Instead add a > > FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked > > page that's in pagecache. Then use the normal page locking and readpage > > logic already in filemap_fault. This simplifies the no page in page > > cache case significantly. > > > > Signed-off-by: Josef Bacik > > Thanks for the patch. I like the simplification but I think it could be > even improved... see below. > > > @@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > > count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); > > ret = VM_FAULT_MAJOR; > > retry_find: > > - page = find_get_page(mapping, offset); > > + page = pagecache_get_page(mapping, offset, > > + FGP_CREAT|FGP_FOR_MMAP, > > + vmf->gfp_mask); > > if (!page) > > - goto no_cached_page; > > + return vmf_error(-ENOMEM); > > So why don't you just do: > > page = pagecache_get_page(mapping, offset, > FGP_CREAT | FGP_LOCK, vmf->gfp_mask); > if (!page) > return vmf_error(-ENOMEM); > goto check_uptodate; > > where check_uptodate would be a label before 'PageUptodate' check? > > Then you don't have to introduce new flag for pagecache_get_page() and you > also don't have to unlock and then lock again the page... And you can still > delete all the code you've deleted. Ah, you don't want lock_page() to block in case someone raced with you and instantiated the page so that you can drop mmap_sem. OK, the patch looks good to me then. You can add: Reviewed-by: Jan Kara Honza -- Jan Kara SUSE Labs, CR
Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
On Fri 07-12-18 10:57:50, Jan Kara wrote: > On Fri 30-11-18 14:58:10, Josef Bacik wrote: > > If we do not have a page at filemap_fault time we'll do this weird > > forced page_cache_read thing to populate the page, and then drop it > > again and loop around and find it. This makes for 2 ways we can read a > > page in filemap_fault, and it's not really needed. Instead add a > > FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked > > page that's in pagecache. Then use the normal page locking and readpage > > logic already in filemap_fault. This simplifies the no page in page > > cache case significantly. > > > > Signed-off-by: Josef Bacik > > Thanks for the patch. I like the simplification but I think it could be > even improved... see below. > > > @@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > > count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); > > ret = VM_FAULT_MAJOR; > > retry_find: > > - page = find_get_page(mapping, offset); > > + page = pagecache_get_page(mapping, offset, > > + FGP_CREAT|FGP_FOR_MMAP, > > + vmf->gfp_mask); > > if (!page) > > - goto no_cached_page; > > + return vmf_error(-ENOMEM); > > So why don't you just do: > > page = pagecache_get_page(mapping, offset, > FGP_CREAT | FGP_LOCK, vmf->gfp_mask); > if (!page) > return vmf_error(-ENOMEM); > goto check_uptodate; > > where check_uptodate would be a label before 'PageUptodate' check? > > Then you don't have to introduce new flag for pagecache_get_page() and you > also don't have to unlock and then lock again the page... And you can still > delete all the code you've deleted. Ah, you don't want lock_page() to block in case someone raced with you and instantiated the page so that you can drop mmap_sem. OK, the patch looks good to me then. You can add: Reviewed-by: Jan Kara Honza -- Jan Kara SUSE Labs, CR
Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
On Fri 30-11-18 14:58:10, Josef Bacik wrote: > If we do not have a page at filemap_fault time we'll do this weird > forced page_cache_read thing to populate the page, and then drop it > again and loop around and find it. This makes for 2 ways we can read a > page in filemap_fault, and it's not really needed. Instead add a > FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked > page that's in pagecache. Then use the normal page locking and readpage > logic already in filemap_fault. This simplifies the no page in page > cache case significantly. > > Signed-off-by: Josef Bacik Thanks for the patch. I like the simplification but I think it could be even improved... see below. > @@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); > ret = VM_FAULT_MAJOR; > retry_find: > - page = find_get_page(mapping, offset); > + page = pagecache_get_page(mapping, offset, > + FGP_CREAT|FGP_FOR_MMAP, > + vmf->gfp_mask); > if (!page) > - goto no_cached_page; > + return vmf_error(-ENOMEM); So why don't you just do: page = pagecache_get_page(mapping, offset, FGP_CREAT | FGP_LOCK, vmf->gfp_mask); if (!page) return vmf_error(-ENOMEM); goto check_uptodate; where check_uptodate would be a label before 'PageUptodate' check? Then you don't have to introduce new flag for pagecache_get_page() and you also don't have to unlock and then lock again the page... And you can still delete all the code you've deleted. Honza -- Jan Kara SUSE Labs, CR
Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
On Fri 30-11-18 14:58:10, Josef Bacik wrote: > If we do not have a page at filemap_fault time we'll do this weird > forced page_cache_read thing to populate the page, and then drop it > again and loop around and find it. This makes for 2 ways we can read a > page in filemap_fault, and it's not really needed. Instead add a > FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked > page that's in pagecache. Then use the normal page locking and readpage > logic already in filemap_fault. This simplifies the no page in page > cache case significantly. > > Signed-off-by: Josef Bacik Thanks for the patch. I like the simplification but I think it could be even improved... see below. > @@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); > ret = VM_FAULT_MAJOR; > retry_find: > - page = find_get_page(mapping, offset); > + page = pagecache_get_page(mapping, offset, > + FGP_CREAT|FGP_FOR_MMAP, > + vmf->gfp_mask); > if (!page) > - goto no_cached_page; > + return vmf_error(-ENOMEM); So why don't you just do: page = pagecache_get_page(mapping, offset, FGP_CREAT | FGP_LOCK, vmf->gfp_mask); if (!page) return vmf_error(-ENOMEM); goto check_uptodate; where check_uptodate would be a label before 'PageUptodate' check? Then you don't have to introduce new flag for pagecache_get_page() and you also don't have to unlock and then lock again the page... And you can still delete all the code you've deleted. Honza -- Jan Kara SUSE Labs, CR
Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
On Fri, Nov 30, 2018 at 02:58:10PM -0500, Josef Bacik wrote: > If we do not have a page at filemap_fault time we'll do this weird > forced page_cache_read thing to populate the page, and then drop it > again and loop around and find it. This makes for 2 ways we can read a > page in filemap_fault, and it's not really needed. Instead add a > FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked > page that's in pagecache. Then use the normal page locking and readpage > logic already in filemap_fault. This simplifies the no page in page > cache case significantly. > > Signed-off-by: Josef Bacik That's a great simplification. Looks correct to me. Acked-by: Johannes Weiner
Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
On Fri, Nov 30, 2018 at 02:58:10PM -0500, Josef Bacik wrote: > If we do not have a page at filemap_fault time we'll do this weird > forced page_cache_read thing to populate the page, and then drop it > again and loop around and find it. This makes for 2 ways we can read a > page in filemap_fault, and it's not really needed. Instead add a > FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked > page that's in pagecache. Then use the normal page locking and readpage > logic already in filemap_fault. This simplifies the no page in page > cache case significantly. > > Signed-off-by: Josef Bacik That's a great simplification. Looks correct to me. Acked-by: Johannes Weiner
[PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
If we do not have a page at filemap_fault time we'll do this weird
forced page_cache_read thing to populate the page, and then drop it
again and loop around and find it. This makes for 2 ways we can read a
page in filemap_fault, and it's not really needed. Instead add a
FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked
page that's in pagecache. Then use the normal page locking and readpage
logic already in filemap_fault. This simplifies the no page in page
cache case significantly.
Signed-off-by: Josef Bacik
---
include/linux/pagemap.h | 1 +
mm/filemap.c| 73 ++---
2 files changed, 16 insertions(+), 58 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 226f96f0dee0..b13c2442281f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -252,6 +252,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
#define FGP_WRITE 0x0008
#define FGP_NOFS 0x0010
#define FGP_NOWAIT 0x0020
+#define FGP_FOR_MMAP 0x0040
struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
int fgp_flags, gfp_t cache_gfp_mask);
diff --git a/mm/filemap.c b/mm/filemap.c
index 81adec8ee02c..f068712c2525 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1503,6 +1503,9 @@ EXPORT_SYMBOL(find_lock_entry);
* @gfp_mask and added to the page cache and the VM's LRU
* list. The page is returned locked and with an increased
* refcount. Otherwise, NULL is returned.
+ * - FGP_FOR_MMAP: Similar to FGP_CREAT, only it unlocks the page after it has
+ * added it to pagecache, as the mmap code expects to do it's own special
+ * locking dance.
*
* If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
* if the GFP flags specified for FGP_CREAT are atomic.
@@ -1555,7 +1558,7 @@ struct page *pagecache_get_page(struct address_space
*mapping, pgoff_t offset,
if (!page)
return NULL;
- if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
+ if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP
fgp_flags |= FGP_LOCK;
/* Init accessed so avoid atomic mark_page_accessed later */
@@ -1569,6 +1572,13 @@ struct page *pagecache_get_page(struct address_space
*mapping, pgoff_t offset,
if (err == -EEXIST)
goto repeat;
}
+
+ /*
+* add_to_page_cache_lru lock's the page, and for mmap we expect
+* a unlocked page.
+*/
+ if (fgp_flags & FGP_FOR_MMAP)
+ unlock_page(page);
}
return page;
@@ -2293,39 +2303,6 @@ generic_file_read_iter(struct kiocb *iocb, struct
iov_iter *iter)
EXPORT_SYMBOL(generic_file_read_iter);
#ifdef CONFIG_MMU
-/**
- * page_cache_read - adds requested page to the page cache if not already there
- * @file: file to read
- * @offset:page index
- * @gfp_mask: memory allocation flags
- *
- * This adds the requested page to the page cache if it isn't already there,
- * and schedules an I/O to read in its contents from disk.
- */
-static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
-{
- struct address_space *mapping = file->f_mapping;
- struct page *page;
- int ret;
-
- do {
- page = __page_cache_alloc(gfp_mask);
- if (!page)
- return -ENOMEM;
-
- ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
- if (ret == 0)
- ret = mapping->a_ops->readpage(file, page);
- else if (ret == -EEXIST)
- ret = 0; /* losing race to add is OK */
-
- put_page(page);
-
- } while (ret == AOP_TRUNCATED_PAGE);
-
- return ret;
-}
-
#define MMAP_LOTSAMISS (100)
/*
@@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
ret = VM_FAULT_MAJOR;
retry_find:
- page = find_get_page(mapping, offset);
+ page = pagecache_get_page(mapping, offset,
+ FGP_CREAT|FGP_FOR_MMAP,
+ vmf->gfp_mask);
if (!page)
- goto no_cached_page;
+ return vmf_error(-ENOMEM);
}
if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
@@ -2488,28 +2467,6 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
vmf->page = page;
return ret | VM_FAULT_LOCKED;
-no_cached_page:
- /*
-* We're only likely to ever get here if MADV_RANDOM is in
-* effect.
-*/
- error = page_cache_read(file,
[PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
If we do not have a page at filemap_fault time we'll do this weird
forced page_cache_read thing to populate the page, and then drop it
again and loop around and find it. This makes for 2 ways we can read a
page in filemap_fault, and it's not really needed. Instead add a
FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked
page that's in pagecache. Then use the normal page locking and readpage
logic already in filemap_fault. This simplifies the no page in page
cache case significantly.
Signed-off-by: Josef Bacik
---
include/linux/pagemap.h | 1 +
mm/filemap.c| 73 ++---
2 files changed, 16 insertions(+), 58 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 226f96f0dee0..b13c2442281f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -252,6 +252,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
#define FGP_WRITE 0x0008
#define FGP_NOFS 0x0010
#define FGP_NOWAIT 0x0020
+#define FGP_FOR_MMAP 0x0040
struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
int fgp_flags, gfp_t cache_gfp_mask);
diff --git a/mm/filemap.c b/mm/filemap.c
index 81adec8ee02c..f068712c2525 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1503,6 +1503,9 @@ EXPORT_SYMBOL(find_lock_entry);
* @gfp_mask and added to the page cache and the VM's LRU
* list. The page is returned locked and with an increased
* refcount. Otherwise, NULL is returned.
+ * - FGP_FOR_MMAP: Similar to FGP_CREAT, only it unlocks the page after it has
+ * added it to pagecache, as the mmap code expects to do it's own special
+ * locking dance.
*
* If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
* if the GFP flags specified for FGP_CREAT are atomic.
@@ -1555,7 +1558,7 @@ struct page *pagecache_get_page(struct address_space
*mapping, pgoff_t offset,
if (!page)
return NULL;
- if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
+ if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP
fgp_flags |= FGP_LOCK;
/* Init accessed so avoid atomic mark_page_accessed later */
@@ -1569,6 +1572,13 @@ struct page *pagecache_get_page(struct address_space
*mapping, pgoff_t offset,
if (err == -EEXIST)
goto repeat;
}
+
+ /*
+* add_to_page_cache_lru lock's the page, and for mmap we expect
+* a unlocked page.
+*/
+ if (fgp_flags & FGP_FOR_MMAP)
+ unlock_page(page);
}
return page;
@@ -2293,39 +2303,6 @@ generic_file_read_iter(struct kiocb *iocb, struct
iov_iter *iter)
EXPORT_SYMBOL(generic_file_read_iter);
#ifdef CONFIG_MMU
-/**
- * page_cache_read - adds requested page to the page cache if not already there
- * @file: file to read
- * @offset:page index
- * @gfp_mask: memory allocation flags
- *
- * This adds the requested page to the page cache if it isn't already there,
- * and schedules an I/O to read in its contents from disk.
- */
-static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
-{
- struct address_space *mapping = file->f_mapping;
- struct page *page;
- int ret;
-
- do {
- page = __page_cache_alloc(gfp_mask);
- if (!page)
- return -ENOMEM;
-
- ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
- if (ret == 0)
- ret = mapping->a_ops->readpage(file, page);
- else if (ret == -EEXIST)
- ret = 0; /* losing race to add is OK */
-
- put_page(page);
-
- } while (ret == AOP_TRUNCATED_PAGE);
-
- return ret;
-}
-
#define MMAP_LOTSAMISS (100)
/*
@@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
ret = VM_FAULT_MAJOR;
retry_find:
- page = find_get_page(mapping, offset);
+ page = pagecache_get_page(mapping, offset,
+ FGP_CREAT|FGP_FOR_MMAP,
+ vmf->gfp_mask);
if (!page)
- goto no_cached_page;
+ return vmf_error(-ENOMEM);
}
if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
@@ -2488,28 +2467,6 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
vmf->page = page;
return ret | VM_FAULT_LOCKED;
-no_cached_page:
- /*
-* We're only likely to ever get here if MADV_RANDOM is in
-* effect.
-*/
- error = page_cache_read(file,
