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    SubjectRe: [PATCH v5 3/3] squashfs: implement readahead
    On Wed, Jun 8, 2022 at 3:29 AM Fabio M. De Francesco
    <fmdefrancesco@gmail.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@infradead.org>
    > > Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
    > > Reported-by: Matthew Wilcox <willy@infradead.org>
    > > Reported-by: Phillip Lougher <phillip@squashfs.org.uk>
    > > Reported-by: Xiongwei Song <Xiongwei.Song@windriver.com>
    > > Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
    > > Reported-by: Andrew Morton <akpm@linux-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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