From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: jianhong chen <chenjianhong2@huawei.com>,
linux-mm@kvack.org, Michal Hocko <mhocko@suse.com>,
Vlastimil Babka <vbabka@suse.cz>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
Michel Lespinasse <walken@google.com>
Subject: mm/mmap.c: fix the adjusted length error
Date: Mon, 8 Mar 2021 18:50:02 +0000 [thread overview]
Message-ID: <20210308185002.GD3479805@casper.infradead.org> (raw)
Hi Andrew,
You have a patch in your tree which I think is a bad idea.
Link: http://lkml.kernel.org/r/1558073209-79549-1-git-send-email-chenjianhong2@huawei.com
The problem it describes is real -- if you chew up all the address
space with 64MB pages, free one and then try to allocate another one, it
will fail. I don't like the solution, though. If memory is fragmented
in a different way from that described by the patch, it will cause us
to walk into rbtree nodes that look like they might be able to satisfy
our allocation, only to find that they cannot, due to alignment issues.
In the worst case, it turns into a linear scan of the address space
instead of logarithmic.
I would prefer to see this solved by doing two passes. The first would
look for a 128MB size hole, as we do now, which is guaranteed to find
us a 64MB hole if it succeeds. If that search fails, then we can fall
back to the 64MB hole search, as done in this patch.
next reply other threads:[~2021-03-08 18:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 18:50 Matthew Wilcox [this message]
2021-03-08 23:15 ` Andrew Morton
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