RE: squashfs performance regression and readahea

["Song, Xiongwei" <Xiongwei.Song@windriver.com>]

Thanks Matthew and Hsin-Yi.  I will test the patch by EOD.

Regards,
Xiongwei

-----Original Message-----
From: Hsin-Yi Wang <hsinyi@chromium.org> 
Sent: Monday, May 9, 2022 3:11 PM
To: Matthew Wilcox <willy@infradead.org>
Cc: Song, Xiongwei <Xiongwei.Song@windriver.com>; phillip@squashfs.org.uk; linux-mm@kvack.org; squashfs-devel@lists.sourceforge.net
Subject: Re: squashfs performance regression and readahea

[Please note: This e-mail is from an EXTERNAL e-mail address]

On Mon, May 9, 2022 at 3:05 PM Hsin-Yi Wang <hsinyi@chromium.org> wrote:
>
> On Mon, May 9, 2022 at 12:45 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Sun, May 08, 2022 at 02:46:40PM +0000, Song, Xiongwei wrote:
> > > I am facing a performance regression on squashfs.  There are many 
> > > squashfs partitions on our board. I am doing the operations below 
> > > on 90 squashfs
> > > partitions:
> >
> > Hi Xiongwei.  Thanks for the report.  Hsin-Ye and I have been 
> > working on this problem off-list.  Hsin-Ye, could you send the latest version?
>
> Hi Matthew,
>
> This is the patch of the latest version. Since it's just being 
> reviewed halfway done, I posted the patch here, or should I send it to 
> the list directly?
>
The indent seems broken when I pasted it here. Resend in the attachment.

> Thanks
>
> From 03558dcaab93ed3c32498eb70c7f2b1382b218d6 Mon Sep 17 00:00:00 2001
> From: Hsin-Yi Wang <hsinyi@chromium.org>
> Date: Sun, 10 Oct 2021 21:22:25 +0800
> Subject: [PATCH] squashfs: implement readahead
>
> Implement readahead callback for squashfs. It will read datablocks 
> which cover pages in readahead request. For a few cases it will not 
> mark page as uptodate, including:
> - file end is 0.
> - current batch of pages isn't in the same datablock or not enough in a
>   datablock.
> Otherwise pages will be marked as uptodate. The unhandled pages will 
> be updated by readpage later.
>
> Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
> ---
>  fs/squashfs/file.c | 72 
> +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 71 insertions(+), 1 deletion(-)
>
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c index 
> 89d492916dea..20ec48cf97c5 100644
> --- a/fs/squashfs/file.c
> +++ b/fs/squashfs/file.c
> @@ -39,6 +39,7 @@
>  #include "squashfs_fs_sb.h"
>  #include "squashfs_fs_i.h"
>  #include "squashfs.h"
> +#include "page_actor.h"
>
>  /*
>   * Locate cache slot in range [offset, index] for specified inode.  
> If @@ -494,7 +495,76 @@ static int squashfs_readpage(struct file 
> *file, struct page *page)
>   return 0;
>  }
>
> +static void squashfs_readahead(struct readahead_control *ractl) {  
> +struct inode *inode = ractl->mapping->host;  struct squashfs_sb_info 
> +*msblk = inode->i_sb->s_fs_info;  size_t mask = (1UL << 
> +msblk->block_log) - 1;  size_t shift = msblk->block_log - PAGE_SHIFT;  
> +loff_t req_end = readahead_pos(ractl) + readahead_length(ractl);  
> +loff_t start = readahead_pos(ractl) &~ mask;  size_t len = 
> +readahead_length(ractl) + readahead_pos(ractl) - start;  struct 
> +squashfs_page_actor *actor;  unsigned int nr_pages = 0;  struct page 
> +**pages;
> + u64 block = 0;
> + int bsize, res, i, index;
> + int file_end = i_size_read(inode) >> msblk->block_log;  int 
> +max_pages = 1UL << shift;
> +
> + readahead_expand(ractl, start, (len | mask) + 1);
> +
> + if (readahead_pos(ractl) + readahead_length(ractl) < req_end) 
> + return;
> +
> + nr_pages = readahead_count(ractl);
> + pages = kmalloc_array(nr_pages, sizeof(void *), GFP_KERNEL); if 
> + (!pages) return;
> +
> + actor = squashfs_page_actor_init_special(pages, nr_pages, 0); if 
> + (!actor) goto out;
> +
> + for (;;) {
> + nr_pages = __readahead_batch(ractl, pages, max_pages); if 
> + (!nr_pages) break;
> +
> + if (readahead_pos(ractl) >= i_size_read(inode) ||
> +     file_end == 0 || nr_pages < max_pages) goto skip_pages;
> +
> + index = pages[0]->index >> shift;
> + bsize = read_blocklist(inode, index, &block); res = 
> + squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
> +
> + if (res >=0 && (pages[nr_pages - 1]->index >> shift) == index) for 
> + (i = 0; i < nr_pages; i++) SetPageUptodate(pages[i]);
> +
> + for (i = 0; i < nr_pages; i++) {
> + unlock_page(pages[i]);
> + put_page(pages[i]);
> + }
> + }
> +
> + kfree(actor);
> + return;
> +
> +skip_pages:
> + for (i = 0; i < nr_pages; i++) {
> + unlock_page(pages[i]);
> + put_page(pages[i]);
> + }
> +
> + kfree(actor);
> +out:
> + kfree(pages);
> +}
>
>  const struct address_space_operations squashfs_aops = {
> - .readpage = squashfs_readpage
> + .readpage = squashfs_readpage,
> + .readahead = squashfs_readahead
>  };
> --
> 2.31.0