linux-kernel - Re: [PATCH] mm: Support madvise_willneed override by Filesystems

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Date:   Wed, 3 Jul 2019 19:21:41 +0200
From:   Jan Kara <jack@...e.cz>
To:     Boaz Harrosh <openosd@...il.com>
Cc:     Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Chinner <dchinner@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-bcache@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Zach Brown <zach.brown@...com>, Jens Axboe <axboe@...nel.dk>,
        Josef Bacik <josef@...icpanda.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Amir Goldstein <amir73il@...il.com>
Subject: Re: [PATCH] mm: Support madvise_willneed override by Filesystems

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@...app.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@...il.com>
> CC: Miklos Szeredi <mszeredi@...hat.com>
> Signed-off-by: Boaz Harrosh <boazh@...app.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@...e.com>
SUSE Labs, CR