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Message-ID: <CAJMQK-jjNRuZFOJrd2knQHwPERaJ64pyys+14cCVyfdsP1GZSQ@mail.gmail.com>
Date: Mon, 16 May 2022 19:04:08 +0800
From: Hsin-Yi Wang <hsinyi@...omium.org>
To: Phillip Lougher <phillip@...ashfs.org.uk>,
Matthew Wilcox <willy@...radead.org>,
Xiongwei Song <Xiongwei.Song@...driver.com>
Cc: Zheng Liang <zhengliang6@...wei.com>,
Zhang Yi <yi.zhang@...wei.com>, Hou Tao <houtao1@...wei.com>,
Miao Xie <miaoxie@...wei.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-mm @ kvack . org" <linux-mm@...ck.org>,
"squashfs-devel @ lists . sourceforge . net"
<squashfs-devel@...ts.sourceforge.net>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] squashfs: implement readahead
On Mon, May 16, 2022 at 6:51 PM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
>
> 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.
> - zero filled blocks.
> - 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.
>
Suggested-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
> Note that this patch was not formally sent to the list before. It's
> attached to email thread for discussion as it's still under development.
>
> - v1:
> The patch outline was suggested by Matthew. It went through a few
> reviews by Matthew offline.
>
> - v2:
> https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#m442435c149d411c5c9d8019cff5915419b04bf10
> This is a resend of v1.
>
> - v3:
> https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#m55a709e6ba5ec59fe95323a67a7f3d6b1953e470
> Fix page actor size to avoid a crash from squashfs_decompress().
> Suggested by Phillip Lougher[1]
> [1] https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#m687f82debb7667ff31982a05aef3eba081eb5039
>
> - v4:
> https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#mf93267690ec2e841dade6a494fe72c84b61328d9
> Fix to free page after used. Suggested by Xiongwei Song[2]
> Refactor the skip page logic to possible improve the performance.
> Suggested by Phillip Lougher[3]
> [2] https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#m0e7b33d167b1ef0eb39b9f41c32ed3f80dfced18
> [3] https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#m1e0a8f8e4a98d79d14c81b66e197b6dc0a3b77a1
> ---
> fs/squashfs/file.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 77 insertions(+)
>
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> index a8e495d8eb86..91dfec792f4c 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
> @@ -495,7 +496,83 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
> 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;
> + unsigned int max_pages = 1UL << shift;
> +
> + readahead_expand(ractl, start, (len | mask) + 1);
> +
> + if (readahead_pos(ractl) + readahead_length(ractl) < req_end ||
> + file_end == 0)
> + return;
> +
> + pages = kmalloc_array(max_pages, sizeof(void *), GFP_KERNEL);
> + if (!pages)
> + return;
> +
> + actor = squashfs_page_actor_init_special(pages, max_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) ||
> + nr_pages < max_pages)
> + goto skip_pages;
> +
> + index = pages[0]->index >> shift;
> + if ((pages[nr_pages - 1]->index >> shift) != index)
> + goto skip_pages;
> +
> + bsize = read_blocklist(inode, index, &block);
> + if (bsize == 0)
> + goto skip_pages;
> +
> + res = squashfs_read_data(inode->i_sb, block, bsize, NULL,
> + actor);
> +
> + if (res >= 0)
> + 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);
> + kfree(pages);
> + 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 = {
> .read_folio = squashfs_read_folio
> + .readahead = squashfs_readahead
> };
> --
> 2.36.0.550.gb090851708-goog
>
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