From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Dongming Liu <ldming101(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: DSA failed to allocate memory |
Date: | 2022-01-24 17:20:02 |
Message-ID: | CA+TgmobzHdsJ1RJHXWd=os2NhcuZhkGTruAffV9cCH207=g1hg@mail.gmail.com |
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On Mon, Jan 24, 2022 at 4:59 AM Dongming Liu <ldming101(at)gmail(dot)com> wrote:
> Maybe we can use one of the following methods to fix it:
> 1. re-bin segment to suitable segment index when called dsa_free
> 2. get_best_segment search all bins
(2) is definitely the wrong idea. The comments say:
/*
* What is the lowest bin that holds segments that *might* have n contiguous
* free pages? There is no point in looking in segments in lower bins; they
* definitely can't service a request for n free pages.
*/
#define contiguous_pages_to_segment_bin(n) Min(fls(n), DSA_NUM_SEGMENT_BINS - 1)
So it's OK for a segment to be in a bin that suggests that it has more
consecutive free pages than it really does. But it's NOT ok for a
segment to be in a bin that suggests it has fewer consecutive pages
than it really does. If dsa_free() is putting things back into the
wrong place, that's what we need to fix.
--
Robert Haas
EDB: http://www.enterprisedb.com
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