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gfs2: Fix should_fault_in_pages() logic

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Fix the fault-in window size logic:
* Use a maximum window size of 1 MiB instead of BIO_MAX_VECS * PAGE_SIZE.
  The previous window size was always one page because the pages variable
  was accidentally being defined and then redefined in
  should_fault_in_pages().
* The nr_dirtied heuristic for guessing when there might be memory
  pressure often results in very small window sizes.  Don't let
  nr_dirtied drop below 8 pages (as btrfs does).
* Compute the window size in units of bytes, not pages.
* Account for page overlap (unaligned iterators).

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
This commit is contained in:
Andreas Gruenbacher 2022-03-07 23:30:03 +01:00
parent b296393234
commit bb7f5d96aa
1 changed files with 9 additions and 8 deletions
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17
fs/gfs2/file.c
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@ -775,8 +775,7 @@ static inline bool should_fault_in_pages(ssize_t ret, struct iov_iter *i,
size_t *window_size)
{
size_t count = iov_iter_count(i);
char __user *p;
int pages = 1;
size_t size, offs;
if (likely(!count))
return false;
@ -785,18 +784,20 @@ static inline bool should_fault_in_pages(ssize_t ret, struct iov_iter *i,
if (!iter_is_iovec(i))
return false;
size = PAGE_SIZE;
offs = offset_in_page(i->iov[0].iov_base + i->iov_offset);
if (*prev_count != count || !*window_size) {
int pages, nr_dirtied;
size_t nr_dirtied;
pages = min_t(int, BIO_MAX_VECS, DIV_ROUND_UP(count, PAGE_SIZE));
size = ALIGN(offs + count, PAGE_SIZE);
size = min_t(size_t, size, SZ_1M);
nr_dirtied = max(current->nr_dirtied_pause -
current->nr_dirtied, 1);
pages = min(pages, nr_dirtied);
current->nr_dirtied, 8);
size = min(size, nr_dirtied << PAGE_SHIFT);
}
*prev_count = count;
p = i->iov[0].iov_base + i->iov_offset;
*window_size = (size_t)PAGE_SIZE * pages - offset_in_page(p);
*window_size = size - offs;
return true;
}