Hi,
On Fri, Jun 10, 2022 at 3:42 PM Phillip Lougher <phillip@xxxxxxxxxxxxxxx> wrote:
>
> On 09/06/2022 15:46, Xiongwei Song wrote:
> > This version is bad for my test. I ran the test below
> > "for cnt in $(seq 0 9); do echo 3 > /proc/sys/vm/drop_caches; echo
> > "Loop ${cnt}:"; time -v find /software/test[0-9][0-9] | xargs -P 24 -i
> > cat {} > /dev/null 2>/dev/null; echo ""; done"
> > in 90 partitions.
> >
> > With 9eec1d897139 reverted:
> > 1:06.18 (1m + 6.18s)
> > 1:05.65
> > 1:06.34
> > 1:06.88
> > 1:06.52
> > 1:06.78
> > 1:06.61
> > 1:06.99
> > 1:06.60
> > 1:06.79
> >
> > With this version:
> > 2:36.85 (2m + 36.85s)
> > 2:28.89
> > 1:43.46
> > 1:41.50
> > 1:42.75
> > 1:43.46
> > 1:43.67
> > 1:44.41
> > 1:44.91
> > 1:45.44
> >
> > Any thoughts?
>
> Thank-you for your latest test results, and they tend to
> imply that the latest version of the patch hasn't improved
> performance in your use-case.
>
> One thing which is becoming clear here is that the devil is in
> the detail, and your results being summaries are not capturing
> enough detail to understand what is happening. They show
> something is wrong, but, don't give any guidance as to what
> is happening.
>
> I think it will be difficult to capture more details from
> your test case. But, detail can be captured from summaries, by
> varying the input and extrapolating from the results.
>
> By that I mean have you tried changing anything, and observed any
> changed results?
>
> For instance have you tried any of the following
>
> 1. Changing the parallelism of your test from 24 read threads.
> Does 1, 2, 4 etc parallel read threads change the observed
> behaviour? In other words is the slow-down observed across
> all degrees of parallelism, or is there a critical point.
>
> 2. Does the Squashfs parallelism options in the kernel configuration
> change the behaviour? Knowing if the number of "decompressors"
> available changes the difference in performance could be important.
>
> 3. Are your Squashfs filesystems built using fragments, or without
> fragments? Rebuilding the filesystems without fragments, and
> observing any different performance, would help to pinpoint
> where the issue lies.
>
> 4. What is the block size used in your Squashfs filesystems. Have
> you tried changing the block size, and seen what effect
> it has on the difference in performance between the patches?
>
> 5. You don't mention where your Squashfs filesystems are stored.
> Is this slow media or fast media? Have you tried moving
> the Squashfs filesystems onto different media and observed
> any difference in performance between the patches?
>
Thanks for your response and inputs. I really appreciated your help.
I can try these things but can't provide the detailed results for
now because I'm busy with a few things, hence It's hard to focus
on this one thing for me.
> The fact of the matter is there are many over-lapping factors
> which affect the performance of Squashfs filesystems (like any
> reasonably complex code), which may be elsewhere. It can only
> take a small change somewhere to have a dramatic affect on
> performance.
>
> This is particularly the case with embedded systems, which
> may be short on CPU performance, short on RAM, and have low
> performance media, and be effectively operating on the "edge".
> It can only take a small change, an update for instance, to
> change from performing well to badly.
Totally agree.
>
> I speak from experience, having spent over ten years in embedded
> Linux as a senior engineer and then as a consultant. I have
> my own horror tales as a consultant, dealing with systems pushed
> beyond the edge (with hacks), and the customer insisting they
> didn't do anything to cause the system to finally break.
>
> Maybe it is off topic here. But, I remember one instance where
> a customer had a system out in the field, which "inexplicably"
> started to lock up every 6 months or so. This system had regular
> updates "over the air", and I discovered the "lock up" only
> started happening after the latest update. It turns out the new version
> of the application had grown a new feature which needed more
> RAM than normal. This feature wasn't used very often, but,
> if it coincided with an infrequent "house-keeping" background task,
> the system ran out of memory and locked up (they had disabled the OOM
> killer). This was so rare it might only coincide after six months. No
> bug, but a slow growth in working set RAM over a number of versions.
>
> In other words we may be looking at a knock-on side effect of
> readahead, which is either caused by issues elsewhere or is
> causing issues elsewhere.
>
> Dealing with it in isolation, as bug in the readahead code is going
> to get us nowhere, looking for something that isn't there.
>
> I'm not saying that this is the case here. But, the more detail
> you can provide, and the more test variants you can provide will
> help to determine what is the problem.
Thanks for your sharing. I will provide detail later.
Regards,
Xiongwei
>
> Thanks
>
> Phillip
>
>
> >
> > Regards,
> > Xiongwei
> >
> > On Mon, Jun 6, 2022 at 11:03 PM Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> >> Signed-off-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
> >> Reported-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> >> Reported-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
> >> Reported-by: Xiongwei Song <Xiongwei.Song@xxxxxxxxxxxxx>
> >> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> >> Reported-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >> ---
> >> 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@xxxxxxxxxxxx/
> >> v3: https://lore.kernel.org/lkml/20220523065909.883444-4-hsinyi@xxxxxxxxxxxx/
> >> v2: https://lore.kernel.org/lkml/20220517082650.2005840-4-hsinyi@xxxxxxxxxxxx/
> >> v1: https://lore.kernel.org/lkml/20220516105100.1412740-3-hsinyi@xxxxxxxxxxxx/
> >> ---
> >> 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);
> >> + }
> >> +
> >> + 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
> >>
> >>
>
