Messages in this thread | | | Date | Fri, 15 Sep 2023 17:36:27 +0200 | Subject | Re: [PATCH 0/6] shmem: high order folios support in write path | From | David Hildenbrand <> |
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On 15.09.23 17:34, Matthew Wilcox wrote: > On Fri, Sep 15, 2023 at 05:29:51PM +0200, David Hildenbrand wrote: >> On 15.09.23 11:51, Daniel Gomez wrote: >>> This series add support for high order folios in shmem write >>> path. >>> There are at least 2 cases/topics to handle that I'd appreciate >>> feedback. >>> 1. With the new strategy, you might end up with a folio order matching >>> HPAGE_PMD_ORDER. However, we won't respect the 'huge' flag anymore if >>> THP is enabled. >>> 2. When the above (1.) occurs, the code skips the huge path, so >>> xa_find with hindex is skipped. >> >> Similar to large anon folios (but different to large non-shmem folios in the >> pagecache), this can result in memory waste. > > No, it can't. This patchset triggers only on write, not on read or page > fault, and it's conservative, so it will only allocate folios which are > entirely covered by the write. IOW this is memory we must allocate in > order to satisfy the write; we're just allocating it in larger chunks > when we can.
Oh, good! I was assuming you would eventually over-allocate on the write path.
-- Cheers,
David / dhildenb
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