From: Zhaoyang Huang <[email protected]>
Kswapd uses GFP_KERNEL as gfp_flag which make the judgment of
context is unexpected. fix it by using current_is_kswapd.
Signed-off-by: Zhaoyang Huang <[email protected]>
---
fs/afs/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/afs/file.c b/fs/afs/file.c
index eb11d04..6c199d5 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -485,7 +485,7 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
* elected to wait */
#ifdef CONFIG_AFS_FSCACHE
if (PageFsCache(page)) {
- if (!(gfp_flags & __GFP_DIRECT_RECLAIM) || !(gfp_flags & __GFP_FS))
+ if (current_is_kswapd() || !(gfp_flags & __GFP_FS))
return false;
wait_on_page_fscache(page);
}
--
1.9.1
Huangzhaoyang <[email protected]> wrote:
[adding linux-cachefs to the cc list]
> Kswapd uses GFP_KERNEL as gfp_flag which make the judgment of
> context is unexpected. fix it by using current_is_kswapd.
>
> Signed-off-by: Zhaoyang Huang <[email protected]>
> ---
> fs/afs/file.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/afs/file.c b/fs/afs/file.c
> index eb11d04..6c199d5 100644
> --- a/fs/afs/file.c
> +++ b/fs/afs/file.c
> @@ -485,7 +485,7 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
> * elected to wait */
> #ifdef CONFIG_AFS_FSCACHE
> if (PageFsCache(page)) {
> - if (!(gfp_flags & __GFP_DIRECT_RECLAIM) || !(gfp_flags & __GFP_FS))
> + if (current_is_kswapd() || !(gfp_flags & __GFP_FS))
> return false;
> wait_on_page_fscache(page);
> }
I have several of these in my fscache-rewrite branch, spread across a number
of filesystems. Should I fix all of them the same way?
fs/9p/vfs_addr.c: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
fs/afs/file.c: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
fs/nfs/file.c: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
fs/nfs/fscache.h: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
David
On Thu, Dec 9, 2021 at 4:26 AM David Howells <[email protected]> wrote:
>
> Huangzhaoyang <[email protected]> wrote:
>
> [adding linux-cachefs to the cc list]
>
> > Kswapd uses GFP_KERNEL as gfp_flag which make the judgment of
> > context is unexpected. fix it by using current_is_kswapd.
> >
> > Signed-off-by: Zhaoyang Huang <[email protected]>
> > ---
> > fs/afs/file.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/afs/file.c b/fs/afs/file.c
> > index eb11d04..6c199d5 100644
> > --- a/fs/afs/file.c
> > +++ b/fs/afs/file.c
> > @@ -485,7 +485,7 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
> > * elected to wait */
> > #ifdef CONFIG_AFS_FSCACHE
> > if (PageFsCache(page)) {
> > - if (!(gfp_flags & __GFP_DIRECT_RECLAIM) || !(gfp_flags & __GFP_FS))
> > + if (current_is_kswapd() || !(gfp_flags & __GFP_FS))
> > return false;
> > wait_on_page_fscache(page);
> > }
>
> I have several of these in my fscache-rewrite branch, spread across a number
> of filesystems. Should I fix all of them the same way?
>
> fs/9p/vfs_addr.c: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
> fs/afs/file.c: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
> fs/nfs/file.c: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
> fs/nfs/fscache.h: if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
>
> David
If the gfp flag here is used for judging kswapd context, I think the
answer is yes as kswapd applied __GFP_DIRECT_RECLAIM.
>
Zhaoyang Huang <[email protected]> wrote:
> > > - if (!(gfp_flags & __GFP_DIRECT_RECLAIM) || !(gfp_flags & __GFP_FS))
> > > + if (current_is_kswapd() || !(gfp_flags & __GFP_FS))
> > > return false;
> > > wait_on_page_fscache(page);
> ...
> If the gfp flag here is used for judging kswapd context, I think the
> answer is yes as kswapd applied __GFP_DIRECT_RECLAIM.
Now I come to look at applying it, I'm not sure whether this change is right.
I don't know if kswapd has anything to do with it. The check is to see if
we're allowed to block at this point - and wait is just for the completion of
a DIO write to disk.
It would seem like gfpflags_allow_blocking() is the right thing to call - and
that should use current_is_kswapd() if appropriate.
David
On Tue, Dec 21, 2021 at 11:01 PM David Howells <[email protected]> wrote:
>
> Zhaoyang Huang <[email protected]> wrote:
>
> > > > - if (!(gfp_flags & __GFP_DIRECT_RECLAIM) || !(gfp_flags & __GFP_FS))
> > > > + if (current_is_kswapd() || !(gfp_flags & __GFP_FS))
> > > > return false;
> > > > wait_on_page_fscache(page);
> > ...
> > If the gfp flag here is used for judging kswapd context, I think the
> > answer is yes as kswapd applied __GFP_DIRECT_RECLAIM.
>
> Now I come to look at applying it, I'm not sure whether this change is right.
>
> I don't know if kswapd has anything to do with it. The check is to see if
> we're allowed to block at this point - and wait is just for the completion of
> a DIO write to disk.
>
> It would seem like gfpflags_allow_blocking() is the right thing to call - and
> that should use current_is_kswapd() if appropriate.
>
> David
According to my understanding, this check is redundant according to
current vmscan logic. For the allocation which deny
__GFP_DIRECT_RECLAIM could NOT have the context reach here as there is
no synchronous reclaiming. while kswapd also has __GFP_DIRECT_RECLAIM
set and would also block on the page's release.
>