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| author | Ryan Roberts <ryan.roberts@arm.com> | 2023-12-01 16:10:45 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-11-17 15:08:58 +0100 |
| commit | 2ad2067e9ffc8b06aa3c9ab5f51507aadd8aa01a (patch) | |
| tree | 6d4cde7b980f34c19d4764837ae5945602982eab /mm/readahead.c | |
| parent | bc8990235fb5b553c0c20b6185fde74ec9f5923c (diff) | |
| download | linux-2ad2067e9ffc8b06aa3c9ab5f51507aadd8aa01a.tar.gz linux-2ad2067e9ffc8b06aa3c9ab5f51507aadd8aa01a.tar.bz2 linux-2ad2067e9ffc8b06aa3c9ab5f51507aadd8aa01a.zip | |
mm/readahead: do not allow order-1 folio
commit ec056cef76a525706601b32048f174f9bea72c7c upstream.
The THP machinery does not support order-1 folios because it requires meta
data spanning the first 3 `struct page`s. So order-2 is the smallest
large folio that we can safely create.
There was a theoretical bug whereby if ra->size was 2 or 3 pages (due to
the device-specific bdi->ra_pages being set that way), we could end up
with order = 1. Fix this by unconditionally checking if the preferred
order is 1 and if so, set it to 0. Previously this was done in a few
specific places, but with this refactoring it is done just once,
unconditionally, at the end of the calculation.
This is a theoretical bug found during review of the code; I have no
evidence to suggest this manifests in the real world (I expect all
device-specific ra_pages values are much bigger than 3).
Link: https://lkml.kernel.org/r/20231201161045.3962614-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 14 |
1 files changed, 6 insertions, 8 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index 7c0449f8bec7..89139a872194 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -514,16 +514,14 @@ void page_cache_ra_order(struct readahead_control *ractl, unsigned int order = new_order; /* Align with smaller pages if needed */ - if (index & ((1UL << order) - 1)) { + if (index & ((1UL << order) - 1)) order = __ffs(index); - if (order == 1) - order = 0; - } /* Don't allocate pages past EOF */ - while (index + (1UL << order) - 1 > limit) { - if (--order == 1) - order = 0; - } + while (index + (1UL << order) - 1 > limit) + order--; + /* THP machinery does not support order-1 */ + if (order == 1) + order = 0; err = ra_alloc_folio(ractl, index, mark, order, gfp); if (err) break; |