Re: [PATCH] mm: Support madvise_willneed override by Filesystems

Jan Kara
2019-07-03T17:21:54Z

On Wed 03-07-19 04:04:57, Boaz Harrosh wrote:
> On 19/06/2019 11:21, Jan Kara wrote:
> <>
> > Yes, I have patch to make madvise(MADV_WILLNEED) go through ->fadvise() as
> > well. I'll post it soon since the rest of the series isn't really dependent
> > on it.
> >
> > Honza
> >
>
> Hi Jan
>
> Funny I'm sitting on the same patch since LSF last. I need it too for other
> reasons. I have not seen, have you pushed your patch yet?
> (Is based on old v4.20)

Your patch is wrong due to lock ordering. You should not call vfs_fadvise()
under mmap_sem. So we need to do a similar dance like madvise_remove(). I
have to get to writing at least XFS fix so that the madvise change gets
used and post the madvise patch with it... Sorry it takes me so long.

Honza
>
> ~~~~~~~~~
> From fddb38169e33d23060ddd444ba6f2319f76edc89 Mon Sep 17 00:00:00 2001
> From: Boaz Harrosh <boazh@netapp.com>
> Date: Thu, 16 May 2019 20:02:14 +0300
> Subject: [PATCH] mm: Support madvise_willneed override by Filesystems
>
> In the patchset:
> [b833a3660394] ovl: add ovl_fadvise()
> [3d8f7615319b] vfs: implement readahead(2) using POSIX_FADV_WILLNEED
> [45cd0faae371] vfs: add the fadvise() file operation
>
> Amir Goldstein introduced a way for filesystems to overide fadvise.
> Well madvise_willneed is exactly as fadvise_willneed except it always
> returns 0.
>
> In this patch we call the FS vector if it exists.
>
> NOTE: I called vfs_fadvise(..,POSIX_FADV_WILLNEED);
> (Which is my artistic preference)
>
> I could also selectively call
> if (file->f_op->fadvise)
> return file->f_op->fadvise(..., POSIX_FADV_WILLNEED);
> If we fear theoretical side effects. I don't mind either way.
>
> CC: Amir Goldstein <amir73il@gmail.com>
> CC: Miklos Szeredi <mszeredi@redhat.com>
> Signed-off-by: Boaz Harrosh <boazh@netapp.com>
> ---
> mm/madvise.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 6cb1ca93e290..6b84ddcaaaf2 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -24,6 +24,7 @@
> #include <linux/swapops.h>
> #include <linux/shmem_fs.h>
> #include <linux/mmu_notifier.h>
> +#include <linux/fadvise.h>
>
> #include <asm/tlb.h>
>
> @@ -303,7 +304,8 @@ static long madvise_willneed(struct vm_area_struct *vma,
> end = vma->vm_end;
> end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
>
> - force_page_cache_readahead(file->f_mapping, file, start, end - start);
> + vfs_fadvise(file, start << PAGE_SHIFT, (end - start) << PAGE_SHIFT,
> + POSIX_FADV_WILLNEED);
> return 0;
> }
>
> --
> 2.20.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR