[PATCH] memcg: set page->private before calling swap_readpage

[PATCH] memcg: set page->private before calling swap_readpage

[Shakeel Butt]

The function swap_readpage() (and other functions it call) extracts swap
entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
skips the swapcache and thus we need to manually set the page->private
with the swap entry before calling swap_readpage().

Signed-off-by: Shakeel Butt <shakeelb@google.com>
Reported-by: Heiko Carstens <hca@linux.ibm.com>
---

Andrew, please squash this into "memcg: charge before adding to
swapcache on swapin" patch.

 mm/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index aefd158ae1ea..b6f3410b5902 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 					workingset_refault(page, shadow);
 
 				lru_cache_add(page);
+
+				/* To provide entry to swap_readpage() */
+				set_page_private(page, entry.val);
 				swap_readpage(page, true);
+				set_page_private(page, 0);
 			}
 		} else {
 			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
-- 
2.31.0.rc2.261.g7f71774620-goog

[PATCH] memcg: set page->private before calling swap_readpage

[Shakeel Butt]

The function swap_readpage() (and other functions it call) extracts swap
entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
skips the swapcache and thus we need to manually set the page->private
with the swap entry before calling swap_readpage().

Signed-off-by: Shakeel Butt <shakeelb@google.com>
Reported-by: Heiko Carstens <hca@linux.ibm.com>
---

Andrew, please squash this into "memcg: charge before adding to
swapcache on swapin" patch.

 mm/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index aefd158ae1ea..b6f3410b5902 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 					workingset_refault(page, shadow);
 
 				lru_cache_add(page);
+
+				/* To provide entry to swap_readpage() */
+				set_page_private(page, entry.val);
 				swap_readpage(page, true);
+				set_page_private(page, 0);
 			}
 		} else {
 			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
-- 
2.31.0.rc2.261.g7f71774620-goog

[PATCH] memcg: set page->private before calling swap_readpage

[Shakeel Butt]

The function swap_readpage() (and other functions it call) extracts swap
entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
skips the swapcache and thus we need to manually set the page->private
with the swap entry before calling swap_readpage().

Signed-off-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Reported-by: Heiko Carstens <hca-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
---

Andrew, please squash this into "memcg: charge before adding to
swapcache on swapin" patch.

 mm/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index aefd158ae1ea..b6f3410b5902 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 					workingset_refault(page, shadow);
 
 				lru_cache_add(page);
+
+				/* To provide entry to swap_readpage() */
+				set_page_private(page, entry.val);
 				swap_readpage(page, true);
+				set_page_private(page, 0);
 			}
 		} else {
 			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
-- 
2.31.0.rc2.261.g7f71774620-goog

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Heiko Carstens]

On Wed, Mar 17, 2021 at 06:59:59PM -0700, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Reported-by: Heiko Carstens <hca@linux.ibm.com>
> ---
> 
> Andrew, please squash this into "memcg: charge before adding to
> swapcache on swapin" patch.
> 
>  mm/memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index aefd158ae1ea..b6f3410b5902 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  					workingset_refault(page, shadow);
>  
>  				lru_cache_add(page);
> +
> +				/* To provide entry to swap_readpage() */
> +				set_page_private(page, entry.val);
>  				swap_readpage(page, true);
> +				set_page_private(page, 0);

Yes, this seems to fix it. Thanks a lot!

Tested-by: Heiko Carstens <hca@linux.ibm.com>

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Heiko Carstens]

On Wed, Mar 17, 2021 at 06:59:59PM -0700, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().
> 
> Signed-off-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Reported-by: Heiko Carstens <hca-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
> ---
> 
> Andrew, please squash this into "memcg: charge before adding to
> swapcache on swapin" patch.
> 
>  mm/memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index aefd158ae1ea..b6f3410b5902 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  					workingset_refault(page, shadow);
>  
>  				lru_cache_add(page);
> +
> +				/* To provide entry to swap_readpage() */
> +				set_page_private(page, entry.val);
>  				swap_readpage(page, true);
> +				set_page_private(page, 0);

Yes, this seems to fix it. Thanks a lot!

Tested-by: Heiko Carstens <hca-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Michal Hocko]

On Wed 17-03-21 18:59:59, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().

One thing that is not really clear to me is whether/why this is only
needed with your patch. Can you expand a bit on that please? Maybe I am
just missing something obvious but I just do not see any connection.

> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Reported-by: Heiko Carstens <hca@linux.ibm.com>
> ---
> 
> Andrew, please squash this into "memcg: charge before adding to
> swapcache on swapin" patch.
> 
>  mm/memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index aefd158ae1ea..b6f3410b5902 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  					workingset_refault(page, shadow);
>  
>  				lru_cache_add(page);
> +
> +				/* To provide entry to swap_readpage() */
> +				set_page_private(page, entry.val);
>  				swap_readpage(page, true);
> +				set_page_private(page, 0);
>  			}
>  		} else {
>  			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
> -- 
> 2.31.0.rc2.261.g7f71774620-goog
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Michal Hocko]

On Wed 17-03-21 18:59:59, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().

One thing that is not really clear to me is whether/why this is only
needed with your patch. Can you expand a bit on that please? Maybe I am
just missing something obvious but I just do not see any connection.

> Signed-off-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Reported-by: Heiko Carstens <hca-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
> ---
> 
> Andrew, please squash this into "memcg: charge before adding to
> swapcache on swapin" patch.
> 
>  mm/memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index aefd158ae1ea..b6f3410b5902 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  					workingset_refault(page, shadow);
>  
>  				lru_cache_add(page);
> +
> +				/* To provide entry to swap_readpage() */
> +				set_page_private(page, entry.val);
>  				swap_readpage(page, true);
> +				set_page_private(page, 0);
>  			}
>  		} else {
>  			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
> -- 
> 2.31.0.rc2.261.g7f71774620-goog
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Johannes Weiner]

On Thu, Mar 18, 2021 at 03:01:25PM +0100, Michal Hocko wrote:
> On Wed 17-03-21 18:59:59, Shakeel Butt wrote:
> > The function swap_readpage() (and other functions it call) extracts swap
> > entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> > skips the swapcache and thus we need to manually set the page->private
> > with the swap entry before calling swap_readpage().
> 
> One thing that is not really clear to me is whether/why this is only
> needed with your patch. Can you expand a bit on that please? Maybe I am
> just missing something obvious but I just do not see any connection.

It was always needed, his original patch erroneously removed it.

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Johannes Weiner]

On Thu, Mar 18, 2021 at 03:01:25PM +0100, Michal Hocko wrote:
> On Wed 17-03-21 18:59:59, Shakeel Butt wrote:
> > The function swap_readpage() (and other functions it call) extracts swap
> > entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> > skips the swapcache and thus we need to manually set the page->private
> > with the swap entry before calling swap_readpage().
> 
> One thing that is not really clear to me is whether/why this is only
> needed with your patch. Can you expand a bit on that please? Maybe I am
> just missing something obvious but I just do not see any connection.

It was always needed, his original patch erroneously removed it.

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Johannes Weiner]

On Wed, Mar 17, 2021 at 06:59:59PM -0700, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Reported-by: Heiko Carstens <hca@linux.ibm.com>

LGTM

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Johannes Weiner]

On Wed, Mar 17, 2021 at 06:59:59PM -0700, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().
> 
> Signed-off-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Reported-by: Heiko Carstens <hca-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>

LGTM

Re: [PATCH] memcg: set page->private before calling swap_readpage

[Michal Hocko]

On Thu 18-03-21 11:02:17, Johannes Weiner wrote:
> On Thu, Mar 18, 2021 at 03:01:25PM +0100, Michal Hocko wrote:
> > On Wed 17-03-21 18:59:59, Shakeel Butt wrote:
> > > The function swap_readpage() (and other functions it call) extracts swap
> > > entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> > > skips the swapcache and thus we need to manually set the page->private
> > > with the swap entry before calling swap_readpage().
> > 
> > One thing that is not really clear to me is whether/why this is only
> > needed with your patch. Can you expand a bit on that please? Maybe I am
> > just missing something obvious but I just do not see any connection.
> 
> It was always needed, his original patch erroneously removed it.

Ahh, I can see it now. I must have been blind. Thanks!

-- 
Michal Hocko
SUSE Labs