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Date: Wed, 8 Jun 2022 18:20:10 +0800
From: Hsin-Yi Wang <hsinyi@...omium.org>
To: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc: Phillip Lougher <phillip@...ashfs.org.uk>,
Matthew Wilcox <willy@...radead.org>,
Xiongwei Song <Xiongwei.Song@...driver.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Zheng Liang <zhengliang6@...wei.com>,
Zhang Yi <yi.zhang@...wei.com>, Hou Tao <houtao1@...wei.com>,
Miao Xie <miaoxie@...wei.com>,
"linux-mm @ kvack . org" <linux-mm@...ck.org>,
"squashfs-devel @ lists . sourceforge . net"
<squashfs-devel@...ts.sourceforge.net>,
linux-kernel@...r.kernel.org, ira.weiny@...el.com
Subject: Re: [PATCH v5 3/3] squashfs: implement readahead
On Wed, Jun 8, 2022 at 3:29 AM Fabio M. De Francesco
<fmdefrancesco@...il.com> wrote:
>
> On lunedì 6 giugno 2022 17:03:05 CEST Hsin-Yi Wang 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.
> > - decompressor error.
> > 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>
> > Reported-by: Matthew Wilcox <willy@...radead.org>
> > Reported-by: Phillip Lougher <phillip@...ashfs.org.uk>
> > Reported-by: Xiongwei Song <Xiongwei.Song@...driver.com>
> > Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > Reported-by: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> > v4->v5:
> > - Handle short file cases reported by Marek and Matthew.
> > - Fix checkpatch error reported by Andrew.
> >
> > v4: https://lore.kernel.org/lkml/20220601103922.1338320-4-hsinyi@chromium.org/
> > v3: https://lore.kernel.org/lkml/20220523065909.883444-4-hsinyi@chromium.org/
> > v2: https://lore.kernel.org/lkml/20220517082650.2005840-4-hsinyi@chromium.org/
> > v1: https://lore.kernel.org/lkml/20220516105100.1412740-3-hsinyi@chromium.org/
> > ---
> > fs/squashfs/file.c | 124 ++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 123 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> > index a8e495d8eb86..fbd096cd15f4 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 +496,128 @@ 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;
> > + unsigned short shift = msblk->block_log - PAGE_SHIFT;
> > + 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;
> > + int i, file_end = i_size_read(inode) >> msblk->block_log;
> > + unsigned int max_pages = 1UL << shift;
> > +
> > + readahead_expand(ractl, start, (len | mask) + 1);
> > +
> > + if (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 (;;) {
> > + pgoff_t index;
> > + int res, bsize;
> > + u64 block = 0;
> > + unsigned int expected;
> > +
> > + nr_pages = __readahead_batch(ractl, pages, max_pages);
> > + if (!nr_pages)
> > + break;
> > +
> > + if (readahead_pos(ractl) >= i_size_read(inode))
> > + goto skip_pages;
> > +
> > + index = pages[0]->index >> shift;
> > + if ((pages[nr_pages - 1]->index >> shift) != index)
> > + goto skip_pages;
> > +
> > + expected = index == file_end ?
> > + (i_size_read(inode) & (msblk->block_size -
> 1)) :
> > + msblk->block_size;
> > +
> > + bsize = read_blocklist(inode, index, &block);
> > + if (bsize == 0)
> > + goto skip_pages;
> > +
> > + if (nr_pages < max_pages) {
> > + struct squashfs_cache_entry *buffer;
> > + unsigned int block_mask = max_pages - 1;
> > + int offset = pages[0]->index - (pages[0]-
> >index & ~block_mask);
> > +
> > + buffer = squashfs_get_datablock(inode->i_sb,
> block,
> > +
> bsize);
> > + if (buffer->error) {
> > + squashfs_cache_put(buffer);
> > + goto skip_pages;
> > + }
> > +
> > + expected -= offset * PAGE_SIZE;
> > + for (i = 0; i < nr_pages && expected > 0; i+
> +,
> > + expected -=
> PAGE_SIZE, offset++) {
> > + int avail = min_t(int, expected,
> PAGE_SIZE);
> > +
> > + squashfs_fill_page(pages[i],
> buffer,
> > + offset *
> PAGE_SIZE, avail);
> > + unlock_page(pages[i]);
> > + }
> > +
> > + squashfs_cache_put(buffer);
> > + continue;
> > + }
> > +
> > + res = squashfs_read_data(inode->i_sb, block, bsize,
> NULL,
> > + actor);
> > +
> > + if (res == expected) {
> > + int bytes;
> > +
> > + /* Last page may have trailing bytes not
> filled */
> > + bytes = res % PAGE_SIZE;
> > + if (bytes) {
> > + void *pageaddr;
> > +
> > + pageaddr =
> kmap_atomic(pages[nr_pages - 1]);
> > + memset(pageaddr + bytes, 0,
> PAGE_SIZE - bytes);
> > + kunmap_atomic(pageaddr);
> > + }
>
> Hi Hsin-Yi,
>
> kmap_atomic() shouldn't be used in new code, unless there are special
> reasons that I am not able to spot here.
>
> Why not use kmap_local_page(), preferably via memzero_page?
Right, these can be replaced with kmap_local_page(pages[nr_pages - 1],
bytes, PAGE_SIZE - bytes);
Thanks for the suggestion.
>
> Thanks,
>
> Fabio
>
> > +
> > + for (i = 0; i < nr_pages; i++) {
> > + flush_dcache_page(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
> > + .read_folio = squashfs_read_folio,
> > + .readahead = squashfs_readahead
> > };
> > --
> > 2.36.1.255.ge46751e96f-goog
> >
> >
> >
>
>
>
>
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