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SubjectCan prune_icache safely discard inodes which have only clean pages? (2.4.18)
Date
I've got a system which has a fairly large amount of physical memory (2GB)
that experiences
performance problems after a large number of files have been accessed.

Looking into the slab_info I discovered that a very large number of inodes
are currently
present in the system (along with many buffer headers). Digging deeper I was
able to determine
that most of the inodes were on the inode_unused chain, but were being
skipped over during
the prunce_icache processing because they have a non-zero number of pages
(i_data.nrpages).
Looking a bit deeper I discovered that most of the inodes had only pages
that are on the
clean_pages list, with these pages also accounting for many of the buffer
heads.

The system wasn't attempting to free these pages (presumably since it still
had a fair
amount of physical memory available, so it didn't need to do this).

Is there any danger in changing prune_icache to also pick an inode for
pruning if it has
a non-zero page count where the dirty_list and locked_list are empty?

In particular, the existing code in fs/inode.c looks somewhat like:

#define CAN_UNUSE(inode) \
((((inode)->i_state | (inode)->i_data.nrpages) == 0) && \
!inode_has_buffers(inode))
void prune_icache(int goal)
{
...
while (entry != &inode_unused)
{
...
if (inode->i_state & (I_FREEING|I_CLEAR|I_LOCK))
continue;
if (!CAN_UNUSE(inode))
continue;

Remove inode from i_hash and add to freeable
}
...
dispose_list(freeable);
...
}

and I'd like to change it to:

void prune_icache(int goal)
{
...
while (entry != &inode_unused)
{
...
if (inode->i_state & (I_FREEING|I_CLEAR|I_LOCK))
continue;
if ((inode->i_state != 0) || inode_has_buffers(inode))
continue;
if (inode->i_data.nrpages != 0) {
if ((!list_empty(&inode->i_data.dirty_pages)) ||
(!list_empty(&inode->i_data.locked_pages))) {
/* skip if any dirty or locked pages */
continue;
}
}

Remove inode from i_hash and add to freeable
}
...
dispose_list(freeable);
...
}


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